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Gas  Power.  By  Professor  C.  F.  HIRSHFELD  and 
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Heat:  A  Text  Book  for  Technical  and  Industrial 
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GAS    POWER 


BY 


C.  F.  HIRSHFELD,  M.M.E. 

Professor  of  Flower  Engineering,  S'Mey  College,   Cornell  University 


AND 


T.  C.  ULBKICHT,  M.M.E. 

Instructor,  Department  of  Power  Engineeriny,  Sibley  College,  Cornell   University 


FIRST    EDITION 

FIRST    THOUSAND 


NEW  YORK 

JOHN     WILEY     &     SONS 

LONDON:    CHAPMAN  &  HALL,  LIMITED 

1913 


Copyright,  1913, 

BY 

C.  F.  HIRSHFELD     AND     T.  C.  ULBRICHT 


THE  SCIENTIFIC    PRESS 

ROBERT    DRUMMONO    AND    COMPANY 

BROOKLYN,    N.    Y. 


PREFACE 


THE  following  pages  are  intended  to  give  the  reader 
such  knowledge  of  the  methods  and  facts  of  gas  power, 
as  may  enable  him  to  appreciate  the  present  commercial 
status  of  this  branch  of  engineering  and,  if  desired,  to  con- 
tinue the  study  of  the  subject  by  means  of  more  advanced 
works. 

The  treatment  has  been  made  as  simple  and  non- 
mathematical  as  possible,  for  the  purpose  of  adapting  it 
to  the  needs  of  students  in  the  higher  classes  of  manual 
training  schools  and  other  institutions  devoted  to  industrial 
education.  The  book  should  also  prove  useful  to  those 
who  wish  to  obtain  a  working  knowledge  in  this  field,  but 
who  have  not  had  the  advantages  of  a  broad  technical 
education. 

C.  F.  H. 

T.  C.  U. 

ITHACA,  N.  Y. 


259672 


CONTENTS 


CHAPTER  I 

PAGE 

THE  HEAT  ENGINE  PROBLEM 1 

1.  Need  of  Mechanical  Power.  2.  Conversion  of  Heat  into 
Mechanical  Energy.  3.  Fuel  a  Source  of  Heat.  4.  Heat 
Engines  and  Heat  Power  Plants. 

CHAPTER  II 

FUELS , 7 

Solid   Fuels:     5.  Wood    and   Vegetable    Fibres.     6.  Coal; 

Formation  and  Classification.     7.  Solid  Wastes. 
Liquid  Fuels:   8.  Petroleum  Products.     9.  Alcohol. 
Gaseous  Fuels:  10.  Natural  Gas.     11.  Artificial  Gases.     12. 

Producer    Gas.     13.     Blast-furnace    Gas.     14.  Water    Gas. 

15.  Mixed    Gas    or    Air    and    Water    Gas.  16.    Carbureted 

Water  Gas.     17.  Retort  Gases.     18.  Oil  Gas. 

CHAPTER  III 

COMPARISON   OF   THE   EXTERNAL    AND    INTERNAL     COMBUSTION 

PRINCIPLES 19 

19.  External  Combustion.     20.  Internal  Combustion. 

CHAPTER  IV 

HISTORICAL  DEVELOPMENT 25 

21.  The  Gun-powder  Engine.  22.  The  Lenoir  Engine.  23. 
Beau  de  Rochas  Cycle.  24.  Otto  and  Langen  Engine. 
25.  The  Brayton  Engine.  26.  The  Otto  Engine  of  1878.  27. 
The  Clerk  Engine.  28.  The  Diesel  Engine. 


vin  CONTENTS 

CHAPTER  V 

PAGE 

FOUR-  AND  TWO-STROKE  OPERATION 34 

29.  Four-stroke  Otto  Cycle.  30.  Actual  Indicator  Card 
for  Four-stroke  Operation.  31.  Practical  Modifications  of 
the  Four-stroke  Diagram.  32.  Two-stroke  Otto  Cycle. 

33.  Practical    Modifications    of  the    Two-stroke    Diagram. 

34.  Comparison   of  Four-stroke  and  Two-stroke  Operation. 

35.  The  Diesel  Engine. 

CHAPTER  VI 

METHODS  OF  COOLING 53 

36.  Necessity  of  Cooling.  37.  Methods  of  Cooling.  38. 
Reclamation  of  Cooling  Water. 

CHAPTER  VII 

GOVERNING  AND  GOVERNORS 63 

39.  Explanation  of  Governing.  40  Methods  Available. 
41.  Hit  and  Miss  Governing.  42.  Methods  Involving  Varia- 
tion of  Cycle.  43.  Quality  Governing.  44.  Quantity  Gov- 
erning. 45.  Advantages  and  Disadvantages  of  Precision 
Governing.  46.  Mixed  Methods. 


CHAPTER  VIII 

IGNITION  SYSTEMS 73 

47.  Historical.     48.  Hot-tube  Ignition.     49.  Electric  Igni- 
tion— Low-  and  High-tension  Systems. 


CHAPTER  IX 

CARBURETING  AND  CARBURETERS 85 

50.  The  Liquid  Fuel  Problem.  51.  Types  of  Gasoline 
Carbureters.  52.  Jet  Carbureters.  53.  Puddle  Carbureters. 
54.  Carbureting  Kerosene. 


CONTENTS  ix 

CHAPTER  X 

PAGE 

GAS  PRODUCERS 96 

55.  Simple  Theory.  56.  Necessity  of  Cooling  and  Methods. 
57.  Types  of  Producers.  58.  Cleaning  Apparatus.  59.  Blast 
Furnace  as  Gas  Producer. 

CHAPTER  XI 

CLASSIFICATION  AND  TYPES  OF  MODERN  ENGINES 115 

60.  Multiplicity  of  Classifications.  61.  Division  on  Basis 
of  Fuel  Used.  62.  Division  on  Basis  of  Use.  63.  Mechanical 
Construction. 

CHAPTER  XII 

MODERN  TYPES  OF  GAS  AND  GASOLINE  ENGINES 122 

64.  The  Pierce  Auto  Engine.  65.  The  Fairbanks-Morse 
Marine  Engine.  66.  The  Foos  Gas  Engine.  67.  The  Besse 
mer  Gas  Engine.  68.  The  New  York  Car  Wheel  Co. 
Engine.  69.  The  Bruce-Macbeth  Gas  Engine.  70.  The 
Buckeye  Gas  Engine. 

CHAPTER  XIII 

MODERN  TYPES  OF  OIL  ENGINES 153 

71.  The  Peterson  Oil  Engine.  72.  The  Hornsby-Akroyd 
Oil  Engine.  73.  The  Muncie  Oil  Engine.  74.  The  Elyria 
Oil  Engine.  75.  The  Diesel  Oil  Engine. 

CHAPTER  XIV 

GAS  ENGINE  AUXILIARIES 173 

76.  Starting  Devices.     77.  Mufflers. 

CHAPTER  XV 

AMERICAN  PRACTICE  IN  THE  RATING  OF  INTERNAL-COMBUSTION 

ENGINES 178 

78.  Explanatory.  79.  Determination  of  Rated  Brake  Horse- 
power. 80.  Determination  of  Bore,  Stroke,  and  R.P.M. 


x  CONTENTS 

CHAPTER  XVI 

PAGE 

METHODS  OF  TESTING 185 

81.  Objects  of  Tests — Necessary  Data — Calorific  Value  of 
Fuel — Quantity  of  Fuel — Measurement  of  D.H.P. — Method 
of  Stating  Results. 

CHAPTER  XVII 

PERFORMANCE  OF  AMERICAN  ENGINES \ . .   189 

82.  Fuel   Consumption.     83.  Thermal   Efficiency   Curves. 
84.  Consumption  of  Lubricating  Oils.     85.  Cooling  Water. 

CHAPTER  XVIII 

PRACTICAL  OPERATION 193 

86.  Sensitiveness  of  Engine.  87.  Effect  of  Jacket  Tem- 
perature. 88.  Effect  of  Varying  Time  of  Ignition.  89. 
Effect  of  Leaky  Piston  and  Valves.  90.  Effect  of  Excessive 
Cylinder  Lubrication.  91.  Timing  of  Valves. 


GAS    POWER 


CHAPTER  I 
THE   HEAT   ENGINE   PROBLEM 

1.  Need  of  Mechanical  Power.  The  continued  advance 
of  civilization  is  practically  dependent  upon  the  increasing 
use  of  mechanical  power.  In  the  early  stages  of  development 
needs  were  simple  and  could  be  supplied  with  no  greater 
expenditure  than  that  of  human  strength.  As  knowledge 
increased,  however,  greater  power  demands  arose.  These 
were  first  met  by  the  use  of  animals  and  later  by  the  har- 
nessing of  wind  and  water. 

Moving  air,  or  wind,  is  uncertain  in  occurrence  and  can 
be  used  to  develop  only  small  amounts  of  power,  so  that 
it  has  never  been  exploited  very  extensively  except  in  the 
familiar  "  wind  mill  "  pump  and  the  picturesque  Dutch 
flour  mill. 

Water,  on  the  other  hand,  can  be  made  to  furnish 
almost  unlimited  quantities  of  power,  and  as  engineering 
knowledge  increases  there  is  a  constantly  growing  tendency 
to  supply  more  and  more  of  the  power  demand  by  means 
of  hydraulic  equipment.  Unfortunately  water-power  sites 
are  generally  not  conveniently  located  in  the  neighborhood 
of  industrial  centers,  the  latter  having  been  chosen  with 


2;  GAS   POWER 

regard  to  the  ready  acquisition  of  raw  materials  and  the 
easy  distribution  of  the  product. 

Such  location  has  been  justified  by  the  fact  that  mechan- 
ical power  can  also  be  obtained,  though  in  a  very  indirect 
way,  from  fuels,  such  as  coal,  and  oil.  The  following 
paragraphs  will  serve  to  briefly  explain  this  process. 

2.  Conversion  of  Heat  Energy  into  Mechanical  Energy. 
Heat  has  been  experimentally  proved  to  be  a  form  of  energy 
by  the  simple  expedients  of  converting  other  forms  of  energy 
into  heat  and  converting  heat  into  other  forms  of  energy. 
The  conversion  of  mechanical  energy  into  heat  is  a  very 
common  phenomenon,  familiar  to  all  in  the  case  of  heat 
evolved  by  friction  at  the  expense  of  mechanical  energy. 
One  of  the  most  familiar  examples  of  this  conversion  is 
the  arresting  of  the  motion  of  a  car  by  means  of  a  brake 
and  the  heating  of  the  brake  as  a  result  of  the  energy 
converted. 

When  such  conversions  occur,  there  is  exactly  the  same 
quantity  of  energy  after  as  before  the  change;  if  all  the  mechan- 
ical energy  is  converted  into  heat  the  quantity  of  heat 
energy  resulting  will  exactly  equal  the  quantity  of  mechanical 
energy  disappearing.  Unfortunately  the  units  which  we 
use  for  the  measurement  of  energy  in  these  two  forms  are 
very  different  and  not  intrinsically  related  in  any  way; 
the  equality  just  mentioned  is  therefore  difficult  to  realize. 

The  unit  of  heat  energy  in  English-speaking  countries 
is  known  as  the  British  thermal  unit  (B.t.u.),  and  may 
be  denned  as  the  quantity  of  heat  necessary  to  raise  the 
temperature  of  one  pound  of  pure  water  one  degree 
Fahrenheit.  This  measurement  is  usually  made  at  39.1°  F. 
(at  which  temperature  water  has  maximum  density),  or  at 
62°  F. 

Work  may  be  termed  the  overcoming  of  a  resistance 
through  a  certain  distance,  and  is  measured  by  the  product 
of  the  resistance  into  the  space  through  which  it  is  over- 
come. The  unit  of  work  in  the  English  measures  is  called 


I.  THE  HEAT  ENGINE  PROBLEM        3 

the  foot-pound,  or  the  amount  of  work  done  in  overcoming 
a  pressure  or  weight  equal  to  one  pound,  through  a  distance 
of  one  foot. 

Joule,  an  English  scientist,  determined  by  experiment 
the  relation  existing  between  a  unit  of  heat  and  a  unit  of 
work.  He  converted  a  measured  quantity  of  mechanical 
energy  into  heat  energy  and  determined  the  amount  of  the 
latter.  Joule  showed  that  one  thermal  unit  equaled  778 
mechanical  units — that  is, 

lB.t.u.  =  778ft.-lb (1) 

The  number  778  is  called  Joule's  equivalent.* 

3.  Fuel  a  Source  of  Heat.  It  may  be  said  that  there  is 
available  an  inexhaustible  supply  of  heat;  such  is  at  least 
the  case  so  far  as  man  is  concerned.  The  source  of  this 
supply  is  the  sun,  to  which,  in  one  way  or  another,  all  the 
heat  now  used  by  man  is  probably  due.  It  has  proved 
to  be  a  rather  difficult  problem  to  directly  convert  into 
mechanical  energy  the  heat  coming  from  the  sun,  so  that 
it  has  been  more  convenient  to  utilize  the  heat  which  has 
been  stored  in  what  are  called  fuels.  In  the  large  majority 
of  cases  this  storing  of  the  sun's  heat  has  probably  occurred 
through  the  phenomena  of  animal  and  vegetable  growth, 
chemical  processes  directly  dependent  upon  light  and  heat 
from  the  sun. 

By  the  term  fuel  is  meant  any  material  which  when 
burned  will  liberate  heat  in  fairly  large  quantities  and 
which  can  be  produced  cheaply  enough  to  make  it  available 
as  a  source  of  heat  for  commercial  purposes.  Familiar 
examples  are  the  various  varieties  of  coal,  the  woods  and 
similar  vegetable  growths,  the  natural  oils  and  their  prod- 

*  There  is  still  some  uncertainty  as  to  the  correct  numerical  value 
of  this  equivalent.  The  value  here  given  is  the  one  most  commonly 
used,  but  recent  determinations  indicate  that  780  would  be  more  nearly 
correct. 


4  GAS   POWER 

ucts,  natural  gas,  etc.  These  will  be  considered  in  detail 
in  the  next  chapter. 

Fuels  can  generally  be  transported  to  industrial  centers 
by  the  same  means  as  are  used  to  bring  in  other  raw  mate- 
rials and  to  carry  away  the  finished  products.  They, 
therefore,  form  a  very  convenient  source  of  power  for  such 
communities. 

4.  Heat  Engines  and  Heat  Power  Plants.  It  is  very 
easy  to  convert  mechanical  energy  into  heat  energy. 
Potential  mechanical  energy,  or  energy  of  a  body  due  to 
its  position,  as  for  example  the  energy  of  a  compressed 
spring  or  of  a  weight  situated  so  that  it  may  fall,  is  easily 
converted  into  kinetic  mechanical  energy,  or  energy  of 
a  body  due  to  its  motion,  and  the  latter,  involving  motion, 
also  involves  friction.  Friction  will  eventually  bring  the 
moving  bodies,  whatever  they  be,  to  rest  and  the  kinetic 
mechanical  energy  will  then  have  been  entirely  converted 
into  heat  energy. 

The  reverse  of  this  process  is  not  in  general  as  easily 
accomplished — in  fact  rather  elaborate  devices  are  required 
when  it  is  desired  to  continuously  convert  heat  into  me- 
chanical energy.  Such  devices  are  known  as  heat  power 
plants,  several  types  of  which  will  be  discussed  in  a  later 
chapter. 

The  operation  of  such  a  power  plant  can  be  illustrated 
diagrammatically  as  in  Fig.  1.  In  this  figure  A  represents 
a  source  of  heat;  that  is,  anything  in  which  heat  is  made 
available  at  a  comparatively  high  temperature  TI. 
The  ordinary  boiler  furnace  is  a  good  example.  B  repre- 
sents the  device  in  which  heat  is  converted  into  mechanical 
energy — in  engineering  language  it  is  an  engine  or  a  heat 
engine.  The  body  C  is  anything  which  can  be  maintained 
at  a  comparatively  low  temperature,  T%,  and  which  can 
receive  heat  from  the  engine.  The  combination  of  A,  B, 
and  C  constitutes  a  heat  power  plant  and  operates  roughly 
in  the  following  manner. 


I.     THE   HEAT  ENGINE  PROBLEM  5 

Heat  flows  from  A  to  the  engine  B  in  quantities  repre- 
sented by  the  width  of  stream  a.  All  this  heat  enters  the 
engine  B  and  part  of  it  is  there  converted  into  mechanical 
energy,  leaving  the  engine  as  represented  by  stream  b. 
The  part  of  the  heat  stream  a  which  is  not  converted  into 
mechanical  energy  remains  in  the  form  of  heat  energy 
and  passes  from  the  engine  to  the  body  C  as  shown  by 
stream  c. 

In  all  heat  power  plants  the  following  two  conditions 
exist : 

1.  The  heat  leaving  the  engine  in  stream  c  is  at  a  lower 


Hot  Body 


Heat  in  Steam 


^  Atmosphere 
Heat  in  (Cold  Body) 
Steam  (C) 


Cold  Body 


FIG.  1. 


temperature  than  that  entering  the  engine  in  stream  a 
and 

2.  The  sum  of  the  quantities  of  mechanical  and  heat 
energy  leaving  the  engine,  i.e.,  the  sum  of  the  streams  c 
and  b,  must  equal  the  heat  energy  entering  the  engine  as 
represented  by  stream  a. 

It  is  obvious  that  the  best  plant  will  be  the  one  which 
converts  the  maximum  amount  of  heat  stream  a  into 
mechanical  energy  as  represented  by  stream  b.  A  measure 
of  the  performance  of  a  plant  is  therefore  obtained  by 
dividing  the  quantity  of  mechanical  energy  (6)  leaving  by 


6  GAS  POWER 

the  quantity  of  heat  energy  (a)  entering.  This  quotient 
is  called  the  thermal  efficiency  of  the  plant — that  is 

Mechanical  Energy  made  available 

Efficiency  = &J  - .       (2) 

Heat  Supplied 

The  nearer  this  fraction  approaches  unity  the  more  nearly 
does  the  plant  convert  into  mechanical  energy  all  of  the 
heat  supplied  and,  therefore,  the  better  it  is  as  a  power 
plant.  It  can  be  shown  that  a  theoretically  perfect  power 
plant  can  under  no  circumstances  have  an  efficiency  as  high 
as  unity — because  it  must  always  reject  heat  as  heat.  Real 
plants  do  not,  of  course,  give  as  good  results  as  theoretical 
considerations  indicate  to  be  possible,  and  real  power  plant 

1  35 

efficiencies   range   from   —   to   about   — -,   that  is,   from 

J.UU  J.UU 

1  to  35  per  cent.  The  best  real  plants  thus  convert  into 
mechanical  energy  about  35  per  cent  of  the  heat  supplied 
and  reject  at  low  temperatrure  the  other  65  per  cent. 

The  practical  bearing  of  these   considerations  on  the 
gas  power  field  will  appear  in  later  chapters. 


CHAPTER  II. 
FUELS. 

IN  Chapter  I,  the  general  term  fuel  was  explained, 
and  various  familiar  examples  cited.  It  was  shown  that 
for  man's  purposes,  it  is  more  convenient  to  utilize  the 
heat  stored  in  fuels  than  to  make  a  direct  conversion 
of  the  sun's  rays.  The  so-called  fuels  fall  into  logical 
groups,  which  will  be  described  briefly  here,  while  those 
bearing  more  directly  on  gas  power  work  will  be  considered 
in  more  detail  in  later  chapters. 

SOLID  FUELS. 

5.  Wood  and  Vegetable  Fibres.  The  processes  of  vege- 
table growth  closely  resemble  processes  which  occur  in  a  mod- 
ern chemical  laboratory.  Water,  drawn  from  the  earth  by 
the  plant,  and  carbon,  in  the  form  of  C02,  drawn  from  the 
atmosphere,  combine  under  the  action  of  the  sun's  rays  to 
form  chemical  combinations  of  which  cellulose  is  the  most 
familiar  example.  The  chemical  composition  of  pure 
cellulose  is,  C  =  44.44  per  cent;  H  =  6.17  per  cent;  O  =  49.39 
per  cent. 

Cellulose  and  other  similar  compounds,  in  combina- 
tion with  plant  juices  and  small  quantities  of  mineral  salts 
and  other  substances,  form  vegetable  materials  such  as 
wood,  leaves,  grasses,  ferns,  mosses,  etc.,  which  can  be  used 
as  fuel  after  proper  treatment.  Wood,  which  is  one  of  the 
most  familiar  examples,  often  contains  as  much  as  40  per 

7 


8  GAS   POWER 

cent  of  water  when  felled,  and  must  be  dried  for  satisfactory 
use. 

When  wood  is  heated  under  conditions  which  partly 
or  entirely  prevent  oxidation,  destructive  distillation  occurs, 
which,  if  continued  to  a  sufficient  extent,  converts  the  wood 
into  what  is  known  as  charcoal,  a  material  containing 
practically  only  carbon  and  the  mineral  salts  originally 
present  in  the  wood  itself. 

6.  Coal.  It  has  been  clearly  proven  that  coal  is  formed 
from  vegetable  materials,  such  as  those  just  described, 
which  accumulated  in  thick  layers  on  the  earth's  surface 
ages  ago,  and  were  later  buried  under  deposits  of  silt  and 
other  earthy  matter. 

The  process  of  formation  of  coal  is  complex,  but  in  brief 
we  may  say  that  coal  is  the  result  of  the  distillation  of  the 
original  vegetable  matter  under  the  action  of  the  natural 
heat  of  the  earth  and  the  heat  generated  in  decomposition. 
Its  ultimate  composition  is  dependent  upon  the  amount  of 
hydrogen  and  other  gases  which  have  been  able  to  escape 
from  the  decomposing  mass. 

Thousands  of  years  ago  a  piece  of  coal  was  a  mass  of 
damp  vegetable  fibre,  a  portion  of  a  peat-bog.  During 
successive  geologic  ages  the  peat-bog  was  submerged  and 
overlaid  with  mud  which  hardened  into  slate.  This  was 
covered  with  glacial  and  alluvial  drift,  and  may  have  been 
tilted  and  upheaved  by  volcanic  action  or  subsidence  of 
the  earth's  crust.  It  was  subjected  to  great  pressures  and 
high  temperatures,  and  underwent  a  more  or  less  complete 
destructive  distillation  under  pressure.  The  products  of 
the  distillation  vary  in  different  localities,  and  with  dif- 
ferent histories,  so  that  we  now  find  materials  varying  all 
the  way  from  the  original  peat,  through  the  lignites,  bitumi- 
nous and  anthracite  coals,  to  graphitic  coal.  The  last  named, 
found  in  Rhode  Island,  has  had  nearly  ail  the  volatile  hydro- 
carbon gases  and  oxygen  driven  off  from  it,  leaving  prac- 
tically only  fixed  carbon  and  ash.  This  carbon  is  in  a  form 


II.     FUELS  9 

which  is  so  hard  to  burn  that  it  finds  no  extensive  use  as  a 
commercial  fuel. 

Coals  are  classified  in  many  ways,  the  most  common 
being  according  to  the  relative  percentages  of  carbon  and 
volatile  matter  contained  in  the  combustible  portion. 
The  following  outline  will  serve  to  indicate  both  the  line 
of  development  and  the  general  classification  of  coals: 

1.  WOOD.     Fresh  vegetable  material,    cellulose,  starch, 
water. 

2.  PEAT.     Vegetable    matter,    consisting    generally    of 
mosses  more  or   less  decomposed  under  water.     Generally 
dried  by  weathering  or  pressure  or  both  before  use. 

3.  BROWN  LIGNITE.     Carbon,   complex  paraffin  hydro- 
carbons and  carbohydrates,  water. 

4.  BLACK  LIGNITE.     Like  the  brown  lignite  but  with 
more  elementary  carbon. 

5.  SUB-BITUMINOUS.     Intermediate    in    grade    between 
the  black  lignite  and  bituminous  proper. 

6.  BITUMINOUS.     Carbon,   complex  hydrocarbons,  with 
carbohydrates   and   no    hygroscopic   water. 

7.  SEMI-BITUMINOUS.     Between   bituminous   and   semi- 
anthracite. 

8.  SEMI- ANTHRACITE.     More    elementary    carbon    than 
(7)  and  no  carbohydrates;    less  of  hydrocarbons  and  these 
simpler. 

9.  ANTHRACITE.     Elementary  carbon  and  simple  hydro- 
carbons. 

10.  GRAPHITIC   ANTHRACITE.     Very   few    hydrocarbons 
left,  and  some  of  the  elementary  carbon  transformed  into 
graphite. 

11.  GRAPHITE.     Final  result. 

A  study  of  the  map  of  the  U.  S.  will  show  the  remark- 
able way  in  which  the  coal  deposits  of  this  country  follow 
in  general  the  table  of  gradations  outlined  above,  viz., 
the  deposit  in  Rhode  Island  and  Massachusetts  of  hard 
graphitic  coal,  high  in  carbon  content  and  low  in  ash,  mois- 


10  GAS  POWER 

ture  and  volatile  matter;  followed  in  Eastern  Pennsylvania 
by  the  great  anthracite  beds  which  grade  off  as  we  pass  on 
to  the  Susquehanna  River  to  the  semi-anthracite  fields. 
These  in  turn  are  succeeded  by  the  large  bituminous  deposits 
of  Western  Pennsylvania,  Eastern  Kentucky  and  Ohio, 
extending  clown  into  Tennessee  and  Alabama;  while  the 
fields  of  Indiana,  Illinois  and  Western  Kentucky  belong 
to  this  same  classification. 

Passing  the  Mississippi,  we  find  a  constantly  decreasing 
quality  of  coal  from  the  standpoint  of  carbon  content, 
which  finally  grades  into  the  lignites  and  peats  of  the  Pacific 
Coast  regions.  While  this  broad  statement  is  true  in  gen- 
eral, it  must  not  be  taken  too  literally,  as  there  are  numerous 
small  fields  of  various  qualities,  erratically  distributed  over 
the  country;  but  the  best  of  the  higher  grade  coals  of  the 
West  do  not  compare  favorably  with  those  of  the  Appalachian 
Mountain  system.  In  Alaska,  bituminous  and  anthracite 
deposits  of  good  quality  are  being  opened. 

7.  Solid  Wastes.     Other  possible  solid  fuels  are  manu- 
facturing and  city  waste,  sawdust,  straw,  shavings,  bagasse 
and  tan-bark,  etc.,  which  materials  can  be  burned  under 
boilers  in  vicinities  where  such  use  results  in  actual  financial 
returns. 

The  modern  methods  used  in  producing  gas  from  these 
solid  fuels,  to  be  used  for  power  purposes  in  an  engine 
cylinder,  will  be  fully  discussed  in  a  later  chapter. 

LIQUID  FUELS. 

8.  Petroleum   Products.     The    most    important    liquid 
fuels  to-day  in  gas-engine  work  are  the  petroleum  products 
which  are  obtained  from  "  oil  "  wells  situated  in  various 
parts  of  the  world,  as  Russia,  Pennsylvania,  Ohio,  West 
Virginia,  California,  and  Texas. 

Crude  Petroleum,  as  it  comes  out  of  the  earth,  is  a  mechan- 
ical mixture  of  many  different  hydrocarbons,  with  some 


II.     FUELS  11 

sulphur  and  other  impurities.  Hence  it  is  to  be  expected 
that  crude  oils  from  various  fields  will  show  compositions 
which  differ  considerably. 

By  the  process  called  refining,  which  is  accomplished 
by  fractional  distillation,  a  series  of  distillates  is  obtained 
running  from  the  very  light  vapors  and  oils  down  through 
the  heavier  liquids,  to  the  final  thick,  tarry  residues.  Each 
succeeding  product,  therefore,  contains  a  number  of  hydro- 
carbons with  contiguous  boiling-points.  Of  these  oils, 
the  various  gasolines,  kerosenes,  and  the  so-called  "  dis- 
tillates," besides  crude  oil  itself,  are  widely  used  for  gas- 
engine  fuels. 

The  first  results  of  crude  oil  distillation  are  very  light 
products,  which  are  easily  vaporized,  and  very  dangerous 
because  an  explosive  mixture  is  quickly  made  when  they 
are  exposed  to  air.  They  have,  therefore,  not  been  used 
to  any  extent  for  internal  combustion  engines. 

Following  the  distillation  of  the  above  mentioned  light 
products,  we  obtain  a  series  of  gasolines  of  varying  gravities 
and  flash  points.  The  first  of  these  is  about  86°  Be.  gasoline,* 
which  is  now  seldom  used  for  power  purposes  because  of  the 
small  quantity  available.  This  is  followed  by  gasoline  of 
higher  specific  gravity  (lower  Be.  number)  arid  lower  flash 
point.  Most  of  the  gasolines  used  in  engines  at  the  present 
time  are  in  the  neighborhood  of  60  to  65  Be. 

The  next  heavier  distillate  following  the  gasolines  is 
kerosene,  which  is  not  used  for  gas  engines  in  this  country 
as  extensively  as  is  gasoline.  It  will  not  so  readily  form  an 
explosive  mixture  with  air  at  ordinary  temperatures,  and 
therefore  requires  more  elaborate  apparatus  when  used  as 
a  fuel  in  internal  combustion  engines. 

There  is  another  group  of  refinery  products  called 
distillates.  These  are  not  as  well  refined  as  kerosene, 

*  This  is  read  86°  Baume  gasoline,  and  means  that  an  instrument 
which  is  called  a  Baume  hydrometer  will  sink  in  the  liquid  to  a  point 
marked  86  on  an  arbitrary  scale  attached  to  the  instrument. 


12 


GAS  POWER 


but    resemble    it    in    their    general    properties.     They    are 
handled  in  the  same  way  for  gas-engine  work. 

Table  No.  1  gives  average  values  of  the  analyses  of 
American  fuel  oils,  as  determined  in  a  recent  investiga- 
tion bv  the  authors. 


TABLE  I 

AVERAGE    VALUES    OF   ANALYSES    OF   AMERICAN    FUEL 

OILS 


Gasoline. 

Kero- 
sene. 

Crude 
Oil. 

Fuel 
Oil. 

Baum£  gravity  

70.2° 
0.704 
82.54 
14.91 
21,271 
19,818 
19,740 
18,500 
193.5 
109.2 
102 
4.3 
1.93 
0.31 
0.09 
93.0 
85.2 
78.8 
73.2 
68.2 
167° 
55° 

47° 
0.863 
84.00 
14.14 
20,892 
19,600 
20,849 
18,755 
189 
110.3 
103.6 
2.3 
1.838 
2.0 
0.23 
94.3 
86.3 
79.7 
74.0 
69.0 
437° 
130° 

18.3° 

0.877 
84.24 
13.44 
20,162 
19,160 
19,560 
18,636 
187 
111.7 
102.3 
3.1 
0.2 
1.93 
0.823 
93.2 
85.3 
78.8 
73.1 
68.2 

0.939 
83.04 
11.58 
19,183 
18,183 
19,121 

178 
110.2 
102 

0.60 

2.82 
0.90 
92.7 
85.0 
78.5 
73.0 
68.2 

Specific  gravity  

Per  cent  carbon  

Per  cent  hydrogen 

Calorific  value  per  Ib.  (calcu- 
lated)    J 

*High 
Low 
High 
Low 
^ound  . 
\High 
/  Low 

Calorific  value  per  Ib.  (actual  " 
by  test)  J 

Theoretical  air,  cubic  ft.  per] 
Calorific  value  per  cubic  foot 
of  mixture,  theoretical  air  .  . 
Oxygen  -j-  nitrogen 

Per  cent  nitrogen 

Per  cent  oxygen 

1.1 
1.2 
1.3 
1.4 
1.5 

Per  cent  sulphur  

Calorific  value  per  cubic  foot 
mixture   (low),   calculated 
with    given   excess    coeffi- 
cient   

Boiling-point  
Flash  point 

*  When  the  heat  of  the  vaporization  of  the  water  vapor  present  in  the  products 
of  combustion  is  not  included  in  the  calorific  or  heating  value  per  pound  or  per 
cubic  foot  of  the?e  gases,  the  result  is  known  as  "  The  Lower  Heating  Value." 
"  The  Higher  Heating  Value  "  includes  this  extra  heat. 

9.  Alcohol.  Ethyl  alcohol  is  not  used  to  any  extent 
in  this  country  as  a  gas-engine  fuel,  but  is  the  most  likely 
successor  of  the  petroleum  products  as  these  become  scarcer. 


II.     FUELS  13 

Results  of  tests  show  that  a  higher  thermal  efficiency  can 
be  obtained  from  alcohol,  due  to  the  higher  compression 
pressures  that  can  be  used.  It  is  also  much  safer  than 
gasoline  as  regards  fire  risks.  Ethyl  alcohol  or  grain 
alcohol  is  made  from  the  fermentation  of  grape  sugar, 
grain,  potatoes,  and  such  substances.  It  should  not  be 
confused  with  methyl  or  wood  alcohol,  which  results  from 
the  distillation  of  wood. 

The  heating  value  (heat  liberated  per  pound  of  alcohol 
burned)  of  ethyl  alcohol  cannot  be  accurately  computed 
from  its  chemical  composition,  and  it  is  therefore  deter- 
mined by  means  of  the  calorimeter.  The  value  of  11,664 
B.t.u.  per  pound  is  most  frequently  used.  Absolute  or  100 
per  cent  ethyl  alcohol  has  a  specific  gravity  of  0.7946  at 
15°  C.  or  59°  F.,  so  that  one  gallon  of  pure  alcohol  weighs 
6.625  Ibs.  One  pound  of  absolute  ethyl  alcohol  requires  9 
Ibs.  of  air  for  its  combustion;  or  111.5  cu.ft.  at  62°  F. 
Absolute  ethyl  alcohol  is  never  sold  for  fuel  purposes, 
but  is  always  diluted  with  water  and  certain  "  denatur- 
ing "  substances.  This  material  is  sold  as  "  denatured  " 
alcohol,  and  generally  contains  about  10  per  cent  of  water 
and  small  quantities  of  methyl  alcohol  and  hydrocarbons 
with  an  unpleasant  odor. 

GASEOUS  FUELS. 

10.  Natural  Gas.  This  gas,  which  issues  from  the 
interior  of  the  earth  in  many  parts  of  the  world,  especially 
in  the  vicinity  of  oil-fields,  is  very  well  adapted  for  use  in 
gas  engines.  It  is  extensively  used  for  this  purpose  in  the 
natural  gas  regions  around  Pittsburgh,  Buffalo,  Indianapolis, 
and  in  the  State  of  Ohio.  Its  chief  constituent  is  marsh  gas 
(CEU),  with  small  amounts  of  hydrogen,  carbon  monoxide, 
and  unsaturated  hydrocarbons. 

Natural  gas  is  also  found  in  West  Virginia,  Kentucky, 
Tennessee,  Colorado  and  California.  Like  the  petroleum 


14  GAS  POWER 

products,  its  composition  varies  constantly,  even  in  the 
same  well,  and  due  to  the  large  amounts  that  have  been 
and  are  still  being  wasted,  the  supply  is  rapidly  diminishing. 
The  average  values  of  analyses  of  American  natural 
gases,  as  given  in  Table  II,  show  the  wide  variation  in  the 
composition  of  this  fuel. 

11.  Artificial  Gases.     In   addition  to  natural  gas,   the 
following  artificial  gases  are  used  for  gas  engine  fuels: 

(a)  Producer  gas;  (6)  Blast-furnace  gas;  (c)  illuminat- 
ing gases;  (d)  Coke-oven  gas;  (e)  Oil  gas.  These  may 
be  roughly  divided  into  two  classes  according  to  the  proc- 
ess of  manufacture  as,  (1)  Producer  gases,  or  those  made 
by  combustion  processes  and  (2)  Retort  gases,  or  those 
made  by  processes  involving  destructive  distillation.  The 
more  important  of  these  gases  are  described  in  the  following 
sections. 

12.  Producer  Gas.     This   is   the   name   given   to   that 
group  of  gases  which  are  generated  by  the  passage  of  oxygen 
(present  either  in  air  or  in  a  mixture  of  steam  and  air) 
through  an  incandescent  bed  of  carbon.     The  gases  com- 
monly known  as  suction  gas,  Dowson,  Riche,  Mond,  Siemens, 
etc.,  are  all  in  this  class  and  similar  in  character.     Ordinary 
producer  gas  is  made  continuously  by  passing  a  mixture 
of    air  and  steam  through  the  fuel,  in  correct  proportions 
to  maintain  a  sufficient  amount  of  heat  to  enable  chemical 
action  to  take  place. 

Producer  gas  may  be  made  from:  (1)  anthracite  coal; 
(2)  bituminous  coal;  (3)  coke;  (4)  lignite;  (5)  oil;  (6) 
peat;  (7)  wood.  Its  manufacture  will  be  discussed  in 
detail  in  a  later  chapter. 

The  compositions  and  heating  values  of  this  gas  as 
made  from  different  fuels  are  given  in  Table  II,  the  values 
given  representing  the  final  average  of  a  large  number  of 
determinations. 

13.  Blast-furnace  Gas.     This   is    the    gas   obtained    as 
a  by-product  during  the  making  of  pig  iron  from  iron  ore. 


II.     FUELS 


15 


TABLE  II 
AVERAGE    VALUES   OF   ANALYSES    OF  AMERICAN    GASES 


Gas. 

Average  Constituents  of  Gas  in  Per  Cent,  Volume. 

Calorific 
Value  by 
Test  per 
Cubic  Foot. 

C02. 

CO. 

H. 

CH4. 

CaHe. 

C2H4. 

CetJ     N. 

O. 

High. 

Low. 

Producer: 

Anthracite.  .  .  . 

6.03 

22.38 

13.38 

1.96 

0.36 

55  .  65 

0.803 

142 

131.3 

Bituminous  .   . 

9.12 

17.54 

11.73 

4.28 



0.36 

57.24 

0.265 

154 

136 

Coke  

4.90 

27.30 

10.07 

1.18 

56.600.550 

133.7 

(125) 

Lignite  

9.43 

18.90 

15.13 

3.65J  

0.424  

52.50 

0.582 

156.4 

*134 

Oil  

4.10 

11.40 

5.57 

5.87J  

3.10 

66.90 

3.060 

*176 

*151 

Peat  

12.40 

21.00 

18.50 

2.20  

0.40 

1111 

45.50 

0.000 

175 

*141 

Wood  

13.90 

20.03 

21.00 

2.79L  . 

I 

0.60 

41.80 

0.185 

138.7 

*128 

Illuminating: 

Water  

4.72 

34.8 

48.81 

4.06 

1.97 

7.16 

0.503 

329 

278 

Carbureted 
water  

2.07 

24.1 

32.40 

23.40 

12.52 

3.75 

0.510 

677 

632 

Coal  or  bench. 

1.21 

6.18 

43.94 

37.78 

5.87 

4.16 

3.50 

0.502 

655 

592 

Natural: 

6.40 

Average  

0.684 

0.647 

10.89 

79.67 

1.26 

5.89 

0.79 

965 

855 

High  hvdrogen 

0.580 

0.730 

20.56 

50.30 

2.07 
0.515 

5.S8 

8.80 

1.13 
0.50 

895 

810 

Low 

0.800 

0.525 

1.92 

91.40 

3.25 

971 

862 

Blast-furnace... 

11.80 

26.75 

3.40 

0.30 

58.8 

0.182 

98.7 

*95.2 

Coke  oven  

2.1 

6.51 

51  .  56 

32.9 

(1.4) 

2.5 

.... 

4.0 

0.36 

598.0 

506 

Oil  gas  

2.79 

4.96 

17.70 

23.60 

18.78 

5.53 

37.55 

0.702 

662.0 

*542 

*  Theoretical  value. 


16  GAS  POWER 

The  blast  furnace  may  be  regarded  as  nothing  more  than 
a  large  producer,  the  coke  or  coal  used  with  the  iron  ore 
being  partly  burned  to  carbon  monoxide  by  the  oxygen 
in  the  air  blast. 

The  gas  given  off  from  the  blast  furnace  contains  from 
23  to  34  per  cent  of  carbon  monoxide,  a  small  amount  of 
hydrogen  and  hydrocarbons  from  the  dissociation  of  water 
and  volatile  matter  in  the  fuel,  some  carbon  dioxide,  and  a 
large  amount  of  nitrogen. 

Because  of  the  small  content  of  carbon  monoxide,  prac- 
tically the  only  combustible  constituent,  blast-furnace 
gas  is  always  of  low  calorific  value,  and  requires  a  much 
greater  cylinder  capacity  than  other  gases.  However, 
its  use  in  gas  engines  has  led  to  great  savings  in  plants 
where  it  was  originally  either  wasted  or  burned  under  steam 
boilers.  Its  calorific  value  (heat  liberated  per  cu.ft.  of 
gas  burned)  varies  from  about  85  to  105  B.t.u.  per  cu.ft. 

14.  Water  Gas.     This  gas  is  produced  by  passing  steam 
through  a  bed  of  incandescent  carbon   (coke),   which  has 
first  been  raised  to  a  high  temperature  by  a  forced  blast 
of  air.     The  steam,  passing  through  the   fuel  bed,  breaks 
up,  forming  hydrogen,  carbon  monoxide  and  carbon  dioxide. 
This  breaking  up  is  accompanied  by  the  absorption  of  heat 
and  tends  to  reduce  the  temperature  so  that  the  process 
must  be  an  intermittent  one. 

15.  Mixed  Gas  or  Air  and  Water  Gas.     This  gas  may 
be  divided  into  two  parts:    that  made  during  the  "  blow," 
during  which  air  only  is  passed  through  the  fuel,  and  that 
made  during  the  "  make,"  during  which  the  fuel  is  supplied 
with  steam  only.     The  "  blow  "  is  a  heating  period  and 
the  "  make  "  a  cooling  period.       Toward  the  end  of  the 
"  blow  "  the  gas  formed  contains  a  large  proportion  of  car- 
bon monoxide  and  is  therefore  combustible.     It  is  some- 
times caught  and  used  under  the  name  of  air  gas. 

The  gas  formed  during  the  "  make,"  consisting  largely 
of  hydrogen  and  carbon  monoxide,  is  properly  known  as 


II.      FUELS  17 

water  gas.     Air  gas  and  water  gas  are  frequently  mixed 
and  used  under  the  name  of  mixed  gas. 

16.  Carbureted   Water  Gas.    This  gas  is  produced  in 
much  the  same  way  as  plain  water  gas,  except  for  the  addi- 
tion of  oil  gas,  which  is  formed  by  spraying  oil  into  a  heated 
brick  chamber,  through  which  the  water  gas  passes.     This 
addition  is   made  for  the  purpose   of   giving  the  latter  illu- 
minating power. 

17.  Retort  Gases.     These   comprise  those   gases  which 
are  generated  by  destructive  distillation  in  closed  retorts, 
some    being   manufactured    for   fuel    and   power   purposes 
only,    and    others    primarily    as    illuminating    gases.     The 
two  principal  retort  gases  are  briefly  described  in  the  fol- 
lowing   paragraphs : 

(a)  Bench  gas,  also  known  as  coal  gas,  town  gas,  or 
illuminating  gas,  is  one  of  the  most  important  of  this  class, 
and  results  from  the  distillation  of  bituminous  coal  in  fire- 
clay retorts. 

Its  calorific  value  varies  with  the  fuel  and  the  process 
of  manufacture,  but  generally  lies  between  525  and  650 
B.t.u.  per  cubic  foot. 

(6)  Coke-oven  gas  is  a  by-product  obtained  during 
the  manufacture  of  coke  in  retort  coke-ovens.  It  is  the 
part  of  the  gas  generated  which  need  not  be  reburned  for 
heating  the  ovens.  So  far  as  its  properties  are  concerned 
it  is  practically  identical  with  the  gas  already  described 
as  bench  gas. 

18.  Oil   Gas.     This  name   is  applied  rather  indiscrimi- 
nately to  the  gases  made  from  crude  or  unrefined  oil,  by  a 
number  of  different  processes.     The  principal  ones  may  be 
roughly    divided    into  producer    gas    processes,   water-gas 
processes,  and  retort-gas  processes. 

The  first  of  these,  namely  the  proclucer-gas  process, 
will  be  considered  in  a  later  chapter.  The  second  very 
closely  resembles  the  carbureted  water  gas  already  described, 
except  that  no  solid  fuel  is  used.  The  gas  has  a  high 


18  GAS  POWER 

calorific  value,  and  a  high  hydrogen  content,  and  is  not 
well  adapted  for  use  as  a  power  gas,  although  it  has  been 
rather  extensively  applied  for  this  purpose  on  the  Pacific 
Coast. 

The  retort  process  is  carried  out  by  properly  heating 
crude  or  partly  refined  petroleum,  or  any  other  oil  composed 
of  hydrocarbons,  in  a  closed  retort,  so  that  "  cracking  " 
(partial .  decomposition)  results  and  hydrocarbons,  which 
are  gaseous  at  atmospheric  pressure  and  temperature,  are 
obtained  while  solid  carbon  is  left  behind  in  the  retort. 
By  the  proper  regulation  of  the  time  and  temperature,  the 
process  of  decomposition  can  be  stopped  at  any  desired 
point. 

Oil  gas  is  not  the  same  as  vaporized  oil,  since  in  the  latter 
the  hydrocarbons  are  unchanged,  and,  if  the  vapor  is  cooler 
a  liquid  will  result. 


CHAPTER  III. 

COMPARISON    OF    THE    EXTERNAL    AND    INTERNAL 
COMBUSTION  PRINCIPLES. 

19.  External  Combustion.  Heat  engines  may,  in  gen- 
eral, be  divided  into  two  great  classes,  viz.,  those  in  which 
the  combustion  of  the  fuel  is  made  to  occur  in  a  receptacle 
outside  the  engine  itself,  and  those  in  which  combustion 
takes  place  directly  within  the  engine. 

The  steam  power  plant  is  an  example  of  the  first  method. 
In  such  plants,  fuel  is  burned  on  a  grate  under,  or  within,  a 
boiler,  and  part  of  the  heat  liberated  is  transferred  to  and 
absorbed  by  the  contained  water.  When  the  temperature 
corresponding  to  the  desired  pressure  is  reached,  boiling 
occurs  and  steam,  containing  the  heat  it  has  received  from 
the  fuel,  passes  through  a  pipe  line  into  an  engine  cylinder. 

This  steam  now  acts  upon  a  piston  in  the  cylinder  and 
part  of  its  heat  energy  is  converted  into  mechanical  energy, 
part  is  radiated,  and  part  is  discharged  in  the  exhaust  steam. 

In  some  plants  the  steam  is  exhausted  into  the  atmosphere 
and  allowed  to  waste,  while  in  others  it  is  condensed  in  an 
apparatus  known  as  a  condenser,  returned  by  means  of  a 
pump  to  the  boiler,  where  it  is  reconverted  into  steam,  and 
then  again  started  on  the  series  of  events  above  described. 

Fig.  2  shows  an  elementary  steam  power  plant  in  which 
the  cycle  of  operations  just  described  can  be  clearly  followed. 
The  energy  stream,  shown  on  the  figure,  represents  to  an 
approximate  scale  the  various  losses  occurring  in  an  external 
combustion  plant. 

19 


20 


GAS  POWER 


III.     EXTERNAL  AND  INTERNAL  COMBUSTION      21 

From  5  to  22  per  cent,  only,  of  the  heat  given  to  the 
steam  in  the  boiler,  is  converted  into  useful  mechanical 
energy  in  the  cylinder;  while  only  about  80  to  90  per  cent 
of  this  is  actually  converted  into  useful  power  at  the  shaft, 
because  of  friction  of  the  engine  parts,  etc.,  between  the 
cylinder  and  fly-wheel. 

It  should  be  further  noted  that  only  a  fraction  of  all 
the  heat  supplied  the  power  plant  in  the  fuel  is  ever  given 
to  the  steam  in  the  boiler.  As  a  net  result,  the  over-all 
thermal  efficiency  in  a  steam  plant,  that  is,  the  heat  equivalent 
of  the  useful  work  done  divided  by  the  heat  value  of  the 
fuel  supplied,  ranges  from  less  than  5  per  cent  in  small  and 
poorly  designed  plants,  to  15  per  cent  in  the  very  best. 

20.  Internal  Combustion.  The  second  class  mentioned 
above  comprises  all  the  heat  engines  or  power  plants  in 
which  a  mixture  of  fuel  and  air  is  ignited  and  burned  within 
the  engine  cylinder. 

Take  as  an  example,  an  engine  such  as  that  shown  in  Fig. 
3,  operating  on  natural  gas,  where  the  fuel  is  mixed  with  a 
proper  amount  of  air  to  form  a  combustible  mixture  and 
is  then  drawn  into  the  cylinder.  This  mixture  is  ignited 
and  burned  within  the  cylinder,  and,  by  a  series  of  processes 
which  will  be  described  later,  part  of  the  heat  thus  liberated 
is  converted  into  mechanical  energy  at  the  piston.  The 
portion  not  thus  converted  is  partly  radiated  and  partly 
exhausted  with  the  burnt  gases. 

While  theory  would  indicate  the  possibility  of  using  an 
apparatus  similar  to  the  condenser  of  a  steam  plant,  and 
thereby  returning  the  gases  to  their  initial  condition  to  be 
used  again,  it  is  practically  simpler  to  throw  away  these 
burned  gases  and  to  charge  the  cylinder  with  a  fresh  supply 
of  mixture  for  the  next  cycle. 

It  will  be  observed  that  by  making  the  combustion 
occur  within  the  engine  cylinder  itself,  the  boiler  and  steam 
pipe  of  a  steam  plant,  and  their  associated  losses,  have 
been  eliminated.  It  will,  therefore,  be  reasonable  to 


22 


GAS  POWER 


III.     EXTERNAL  AND  INTERNAL  COMBUSTION      23 

expect  an  internal  combustion  engine  of  this  type  to  have 
a  higher  thermal  efficiency  than  that  of  a  steam  plant. 

That  this  is  really  true  in  practice  is  shown  by  the  fact 
that  engines  of  this  kind  give  thermal  efficiencies  ranging 
from  15  to  30  per  cent. 

Now  consider  a  complete  producer-gas  power  plant, 
where  the  fuel  gas  is  artificially  manufactured  in  a  producer, 
then  cleaned  thoroughly  to  eliminate  all  dust,  and  either 


FIG.  4. — Elements  of  a  Producer-gas  Power  Plant. 

carried  directly  over  to  an  engine  in  the  case  of  a  suction 
type  plant,  or  stored  in  a  gas  holder,  in  the  case  of  a  pressure 
type  plant.  A  suction  type  plant  is  shown  in  Fig.  4,  with 
the  corresponding  energy  stream  on  which  the  offshoots 
represent  the  various  losses  from  producer  to  engine. 

From  this  it  is  seen  that,  even  with  the  extra  losses  due 
to  the  addition  of  the  producer,  the  final  "  useful  energy 
delivered  "  is  greater  than  in  the  case  of  the  steam  engine 
plant.  In  other  words,  for  a  given  number  of  heat  units 


24  GAS  POWER 

supplied,  a  larger  number  are  converted  into  useful  energy 
at  the  crank  shaft  in  an  internal  combustion  type  plant,  than 
in  one  of  the  external  combustion  type. 

This  is  partly  due  to  the  fact  that  producers  generally 
have  a  higher  thermal  efficiency  than  do  boilers,  but  to  a 
greater  extent  to  the  fact  that  the  processes  carried  on  in 
the  cylinder  of  the  internal  combustion  engine  are  more 
nearly  perfect  as  energy  converters  than  are  those  used 
in  a  steam  engine.  This  is  due  to  the  higher  temperature 
attained  by  the  working  substance,  which  can  be  shown 
to  be  a  measure  of  the  efficiency  of  all  such  conversions. 

It  should  not  be  inferred,  however,  that  the  internal 
combustion  principle  should  always  be  used  because  it  is 
more  economical  in  the  use  of  fuel,  as  there  are  numberless 
cases  where  local  conditions,  cost  of  fuel,  water,  materials, 
etc.,  demand  the  use  of  a  steam  power  plant,  and  where  a 
producer  or  other  internal  combustion  plant  would  probably 
result  in  financial  failure. 


CHAPTER    IV. 

HISTORICAL  DEVELOPMENT    OF   INTERNAL 
COMBUSTION. 

21.  The  Gunpowder  Engine.  The  modern  internal 
combustion  engine  cannot  be  said  to  have  been  the  inven- 
tion of  any  one  man,  but  is  the  result  of  long  years  of  develop- 
ment by  many  inventors.  It  is  to  the  combined  efforts 
of  numerous  investigators,  whose  judgment  and  foresight 
convinced  them  of  the  great  possibilities  of  a  commercial 
machine  of  this  type,  that  we  owe  the  success  of  the  internal 
combustion  engine  as  it  exists  to-day. 

The  first  internal  combustion  engine  is  credited  to  one 
Abbe  Hautefeuille,  who,  in  1678,  conceived  the  idea  of 
burning  a  small  quantity  of  gunpowder  in  a  chamber  con- 
nected with  a  reservoir  of  water.  After  combustion,  the 
gases  were  cooled,  resulting  in  a  partial  vacuum,  and  the 
water  was  raised  from  the  reservoir  by  atmospheric  pres- 
sure. A  few  years  later  he  described  another  engine  in 
which  the  actual  explosive  energy  of  the  powder  was  used 
to  raise  water  through  a  system  of  pipes  and  check-valves. 
In  this  type  the  water  acted  as  a  piston,  so  that  this  is  the 
first  record  of  a  direct-acting  engine.  It  appears  that 
Hautefeuille  did  not  construct  any  engines  based  on  these 
principles.  In  1690,  one  Papin  improved  upon  the  design 
and  actually  constructed  an  engine  to  work  on  the  above 
principle;  but  because  of  the  crude  materials  and  poor 
workmanship  of  those  early  days,  the  powder  engine  was 
abandoned  as  an  impracticable  machine,  and  it  was  not  until 
after  Watt  had  developed  and  improved  the  steam  engine, 

25 


26  GAS  POWER 

that  we  hear  of  any  more  attempts  to  obtain  patents  for 
engines  of  the  internal  combustion  type. 

In  1791  a  patent  was  granted  to  John  Barber,  an 
Englishman,  for  an  engine  which  operated  on  the  gas  tur- 
bine principle,  and  in  1794  John  Street,  also  an  English- 
man, obtained  a  patent  for  a  machine  operated  by  the  use 
of  vapor  derived  from  a  liquid  fuel  and  air,  ignited  by  a 
flame,  and  exploded  in  a  suitable  cylinder. 

22.  The  Lenoir  Engine.     It  was  not,  however,  until  1860, 
that  the  first  practicable  gas  engine  to  attain  any  marked 
degree    of    commercial    success  was    produced.     This  was 
patented   by   Lenoir,   a  Frenchman,   and  belongs  to  that 
class   in  which   the  charge,   not  precompressed,    maintains 
almost    constant    volume    during    combustion.      In    this 
engine,  the  first  part  of  the  stroke  was  used  for  drawing 
in  the   fresh   charge,  which  was  ignited   while    the   piston 
was  in  motion  near  the  center  of  the  stroke.     Only  the 
latter  half  of  the  stroke  was  therefore  available  for  power 
development.     Fig.   5  shows  sections  of  a  Lenoir  engine, 
and  also  a  theoretical  indicator  diagram  for  this  machine. 
It  is  worthy  of  note  that  this  engine  was  made  double  acting 
and  fitted  with  electric  ignition. 

Hugon,  a  few  years  later,  improved  on  the  Lenoir 
engine,  and  brought  out  a  machine  in  which  the  electric 
ignition  of  Lenoir  was  replaced  by  flame  ignition,  which 
was  considered  more  reliable  at  that  time  than  the  electric 
current. 

23.  Beau  de  Rochas'  Cycle.     It  remained,  however,  for 
Beau  de  Rochas,  in  1862,  to  describe  an  engine  which  was 
later   to   receive   world- wide   notoriety   and   use.     In   this 
engine  the  charge  passed  through  four  distinct  phases  in 
one  cycle  of   operations.     These   were    briefly   as   follows: 
The  charge  was  drawn  into  the  cylinder  during  the  first 
forward  stroke  of  the  piston,  compressed  during  the  return 
stroke,  ignited  and  burned  at  the  beginning  of  the  second 
forward  or  the  expansion  stroke,  and  the  burnt  gases  expelled 


IV.     DEVELOPMENT  OF  INTERNAL  COMBUSTION    27 


28  GAS  POWER 

on  the  second  return  stroke.  Beau  de  Rochas  did  not 
construct  an  engine  illustrating  his  ideas,  which  conse- 
quently passed  unnoticed  for  about  fifteen  years. 

24.  Otto  and  Langen.  In  1861,  N.  A.  Otto  of  Deutz, 
Germany,  attempted  to  improve  upon  Lenoir's  engine  by 
giving  it  a  full-power  stroke.  During  his  investigations 
he  conceived  the  idea  of  compressing  the  charge  by  reversing 
the  motion  of  the  fly-wheel,  and  of  then  igniting  it  by  a 
spark.  As  a  result,  the  sudden  impulse  given  to  the  engine 
caused  it  to  spin  for  several  minutes.  Thus  he  practically 
reproduced  two  of  the  strokes  of  the  modern  four-stroke 
engine.  Practical  difficulties  in  this  engine,  however, 
caused  him  to  turn  aside  and  invent  an  entirely  different 
type  of  machine,  which  is  known  as  the  "  free-piston " 
engine. 

In  this  new  engine,  which  was  built  in  conjunction 
with  Langen,  flame  ignition  was  used  and  much  better 
economy  was  obtained  than  with  the  earlier  types.  In 
Fig.  6  is  shown  a  section  of  the  Otto-Langen  free-piston 
machine,  which  consists  of  a  tall  vertical  cylinder,  water- 
jacketed  through  a  part  or  the  whole  of  its  length,  and  with 
the  top  open  to  the  air.  After  admitting  the  charge  below 
the  piston,  the  igniting  flame  causes  combustion  of  the 
mixture,  which  projects  the  piston  upward  with  high  velocity. 
The  piston  is  connected  with  a  rack,  which  engages  with  a 
gear  attached  to  the  fly-wheel  shaft.  This  gear  turns 
freely  on  the  shaft  while  the  piston  is  moving  upward,  but 
becomes  connected  with  it  by  means  of  a  clutch  when  the 
piston  moves  downward.  The  admission,  ignition,  and 
exhaust  are  controlled  by  a  slide  valve  which  is  regulated 
by  the  governor. 

As  the  piston  is  driven  upward  by  the  pressure  generated 
by  the  burning  charge,  the  pressure  beneath  it  rapidly 
drops  by  expansion,  until  it  becomes  less  than  atmospheric 
at  the  end  of  the  up-stroke.  Due  to  the  unbalanced  pres- 
sures above  and  below  it,  the  piston  is  now  forced  down- 


IV.     DEVELOPMENT  OF  INTERNAL  COMBUSTION     29 

ward,  and  as  it  descends,  the  clutch  engages  with  the  shaft 
and  performs  work.  A  port  in  the  valve  allows  for  the 
exhaust  of  the  burnt  gases. 

After  the  commercial  introduction  of  the  free  piston 
engine,    Otto   developed   a  type  which,   in  modified  form, 


FIG.  6. — Otto  and  Langen's  Free-piston  Engine. 

exists  at  the  present  day.     It  is  described  in  detail  in  a 
later  paragraph. 

25.  The    Brayton    Engine.      The    first   successful   gas 
engine  proper  to  be  constructed  in  the  United   States  was 


30 


GAS  POWER 


patented  by  Geo.  B.  Brayton  in  1872  and  1874.  It  was 
the  first  machine  designed  for  combustion  at  constant 
pressure.  It  was  a  vertical  type  engine  as  shown  in  Fig. 


\i/ 


FIG.  7. — Brayton  Engine. 


7,  and  consisted  of  a  power  cylinder,  P,  and  a  separate 
charging  or  air-compressor  cylinder,  C,  the  pistons  being 
connected  by  a  walking  beam. 

In  this  engine,  the  air  and  fuel  were  supplied  to  the 


IV.     DEVELOPMENT  OF  INTERNAL  COMBUSTION     31 

working  cylinder  under  pressure  for  a  portion  of  the  stroke, 
combustion  continuing  during  the  entire  admission  of 
the  charge  and  causing  an  increase  of  volume  without 
change  of  pressure.  After  sufficient  combustible  had  entered, 
the  supply  valve  closed,  and  the  stroke  of  the  piston  was 
completed  by  the  expansion  of  the  burned  gases.  A  con- 
stantly burning  flame  at  the  head  of  the  power  cylinder 
caused  ignition,  and  wire  diaphragms  were  used  to  keep  the 
flames  from  striking  back. 

26.  The  Otto  Engine.  In  1878,  at  the  Paris  Exposi- 
tion, Otto  exhibited  a  new  engine,  which  operated  practically 
on  the  old  Beau  de  Rochas  cycle.  The  engine  was  rec- 
ognized immediately  as  superior  to  any  of  its  predecessors 
because  of  its  economy  and  capacity  for  a  given  weight, 
and  because  of  its  regularity  of  operation. 

In  Fig.  8,  are  shown  a  horizontal  cross-section,  a  side 
view,  and  an  end  view  of  the  Otto  engine  of  1884. 

The  operating  principles  of  the  Otto  engine  may  be  explained 
with  the  help  of  this  figure.  Assume  that  the  piston  is 
just  beginning  its  suction  stroke,  the  poppet  exhaust  valve, 
Ej  having  just  closed.  As  the  piston  moves  outward, 
only  air  is  drawn  in  through  port  /  for  the  first  part  of  the 
stroke  because  the  gas  valve,  G,  has  not  yet  been  opened 
by  the  cam,  C.  A  moment  later,  the  gas  valve,  G,  opens, 
and  the  mixture  is  admitted  during  the  rest  of  the  stroke. 
At  the  outer  dead  centre,  the  slide  valve,  >S,  has  closed  the 
port,  /,  in  the  head,  and  compression  begins.  When  the 
piston  reaches  the  inner  dead  centre,  the  ignition  cavity, 
K,  is  exposed  and  the  charge  is  ignited.  The  piston 
moves  outward  again  with  expansion  of  the  gases, 
and  on  the  next  (return)  stroke  these  are  exhausted 
through  the  valve  E,  which  has  been  opened  by  the 
cam  C'. 

Economy  tests  on  early  Otto  engines  gave  thermal 
efficiencies  on  the  brake  of  from  9  to  12  per  cent,  while 
one  experimenter  obtained  a  value  of  15.5  per  cent. 


32 


GAS  POWER 


IV.     DEVELOPMENT  OF  INTERNAL  COMBUSTION     33 

27.  The    Clerk    Engine.    The  obvious  disadvantage  of 
the  Otto  type,  which  gave  only  one  impulse  in  four  strokes, 
combined    with    the    fact    that    Otto's    patents    prevented 
others  from  copying  his  engine,  led  experimenters  to  turn 
their  attention  to  the  development  of  an  engine  operating 
on  the  two-stroke  principle,  in  which  there  should  be  an  im- 
pulse   every    second    stroke    or    every    complete    revolution. 
Theoretically  for  a  given  engine,  the  power  should  be  exactly 
doubled,  since  there  would  be  twice  as  many  impulses  as 
in  the  four-stroke  type,  but  this  has  never  been  attained 
in  practice. 

Clerk  produced  the  first  commercial  two-stroke  machine 
in  1880,  but  the  practical  difficulties  which  were  presented 
were  so  great  that  attention  was  again  turned  to  the  develop- 
ment of  the  four-stroke  engine,  and  it  was  not  until  some 
ten  or  twelve  years  later  that  two-stroke  operation  was 
commercially  successful. 

28.  The    Diesel    Engine.     Most    of    the    development 
since  the  time  of  Otto  has  been  directed  toward  the  im- 
provement of  his  engine  or  to  the  production  of  a  similar 
cycle  in  two-strokes  instead  of  four.       There   is,  however, 
one  very  marked  exception.     In  1893  Dr.  Rudolph  Diesel 
of  Germany  invented  a  radically  different  type,  operating 
on  a  cycle  somewhat  similar  to  that  of  Brayton,  though  in 
a  much  more    perfect    manner.     This  engine  has  become 
very  prominent  during  the  past  decade  and  is  considered 
in  detail  in  a  later  section. 


CHAPTER  V. 
FOUR-  AND  TWO-STROKE  OPERATION. 

29.  Four-stroke  Otto  Cycle.  Having  shown  briefly  in 
Chapter  IV  the  series  of  operations  comprising  the  four- 
stroke  Otto  cycle  of  events,  we  are  now  enabled  to  study 
this  cycle  in  more  detail,  by  the  use  of  a  theoretical 
indicator  diagram  such  as  would  be  obtained  from  an  ideal- 
ized engine. 

The  indicator  diagram  is  merely  a  convenient  means  of 
picturing  what  occurs  within  the  cylinder  of  an  engine 
during  operation.  It  gets  its  name  from  the  fact  that 
such  diagrams  can  be  drawn  mechanically  for  real,  operating 
engines  by  means  of  an  instrument  called  an  indicator. 
Such  diagrams  are  very  useful,  as  they  enable  the  engineer 
to  determine  many  things  about  the  operation  of  an  engine 
which  he  cannot  really  see  and  which  it  is  desirable  that  he 
should  know. 

The  diagram  is  drawn  on  a  sheet  of  paper  or  on  a  card 
on  which  vertical  distances  represent  pressure  to  some 
convenient  scale  and  horizontal  distances  represent  volume. 
The  diagram  can  be  obtained  for  an  ideal  case  by  plotting 
a  series  of  points  so  located  on  the  sheet  that  the  vertical 
distances  to  those  points  represent  the  pressures  of  the 
material  within  the  engirie  cylinder  at  the  times  when  the 
volumes  occupied  by  that  material  are  as  shown  by  the 
horizontal  distances  to  the  points.  The  development  of 
such  diagrams  will  be  shown  in  greater  detail  in  the  follow- 
ing paragraphs. 

34 


V.      FOUR-  AND  TWO-STROKE  OPERATION 


35 


Returning  now  to  the  consideration  of  the  four-stroke 
Otto  cycle,  imagine  an  engine  cylinder  as  shown  in  Fig. 
9,  with  an  inlet  valve,  7,  and  an  exhaust  valve,  E.  Both 
these  valves  are  located  in  the  head  and  open  inwardly. 
Assume  that  the  piston  is  at  its  extreme  left,  dead  centre 
position,  that  a  cycle  has  just  been  completed,  and  that 
the  clearance  space  between  the  cylinder  head  and  the  face 
of  the  piston  is  filled  with  burned  gases  (products  of  com- 
bustion) at  atmospheric  pressure. 


FIG.  9. — Idealized  Otto  Diagram  and  Engine. 


Let  the  admission  valve,  /,  now  open,  the  exhaust 
valve,  E,  remaining  closed,  while  the  piston  moves  to  the 
right  on  the  first  stroke  of  the  cycle.  A  charge  of  com- 
bustible mixture  will  be  drawn  into  the  cylinder  where  it 
will  mix  with  the  burnt  gases,  the  mixture  filling  the  cylin- 
der at  atmospheric  pressure.  Since  the  pressure  has  re- 
mained constant  (and  equal  to  atmospheric)  while  the  piston 
has  moved  out  and  opened  up  the  entire  working  volume  of 
the  cylinder,  the  successive  steps  of  this  process  could  be 
shown  by  a  series  of  points  at  constant  height  (equal  to 
atmospheric  pressure)  and  at  such  horizontal  distances  as 


36  GAS   POWER 

to  represent  volumes  varying  from  that  of  the  clearance  to 
that  of  the  clearance  plus  the  volume  of  the  working 
cylinder.  By  joining  these  points  the  line  ed  of  Fig.  9 
would  be  obtained.  It  would  represent  the  pressures 
existing  within  the  cylinder  while  the  piston  moved  from 
the  beginning  to  the  end  of  the  first  or  suction  stroke. 

Now  let  the  inlet  valve  close  and  the  piston  move  to 
the  left  "on  its  second  stroke.  The  charge  is  compressed 
until  it  fills  the  clearance  volume.  The  compression  may 
be  assumed  to  be  adiabatic,  that  is  without  loss  or  gain  of 
heat,  as  heat,  which  would  be  true  only  in  the  ideal  case. 
During  such  a  process  the  pressure  would  rise  as  the  piston 
moved  in,  that  is,  as  the  volume  occupied  by  the  gaseous 
mixture  decreased.  Plotting  points  to  represent  the  succes- 
sive corresponding  pressures  and  volumes  would  then  give 
a  curve  similar  to  da  in  the  figure. 

At  the  point  a  the  charge  is  ignited  by  an  electric  spark 
or  other  means,  and  combustion  follows,  while  the  piston 
is  assumed  to  remain  stationary  at  the  end  of  the  stroke. 
The  heat  energy  liberated  would  raise  the  temperature 
of  the  burning  gases,  and  since  these  are  confined  in  such 
a  way  as  to  maintain  their  volume  constant,  the  increase 
in  temperature  would  be  accompanied  by  an  increase  of 
pressure.  The  increase  of  pressure  at  constant  volume  is 
shown  by  the  line  ab  on  the  diagram. 

This  increased  pressure  now  causes  the  piston  to  move 
outward  on  its  third  stroke,  while  the  gases  expand  adiabat- 
ically  (in  the  ideal  case)  behind  the  piston.  This  expansion 
is  merely  a  gradual  decrease  of  pressure  as  the  volume 
increases  because  of  the  outward  movement  of  the  piston; 
it  would  be  shown  by  a  dropping  curve  such  as  be  in  the 
diagram. 

At  c  the  exhaust  valve,  Ey  is  opened,  and  the  gas  blows 
out  into  the  atmosphere  while  the  piston  remains  stationary 
at  the  end  of  the  stroke.  This  is  shown  by  the  line  cd  on 
the  diagram,  the  pressure  within  the  cylinder  dropping 


V.      FOUR-  AND  TWO-STROKE  OPERATION          37 

to  atmospheric  (in  the  ideal  case)  before  the  piston 
moves. 

The  piston  then  returns,  executing  its  fourth  stroke,  and 
expels  the  remaining  gas  along  the  line  de,  that  is,  it  drives 
the  gases  out  at  atmospheric  pressure,  thus  decreasing  the 
volume  in  the  cylinder  while  the  pressure  remains  constant. 
When  the  piston  finishes  this  stroke,  that  is,  when  the 
conditions  are  as  shown  at  e,  the  cycle  is  completed,  for 
everything  is  in  the  same  condition  as  assumed  at  the  start. 

While  it  is  beyond  the  scope  of  this  book  to  furnish  the 
proof,  it  is  comparatively  easy  to  show  that  area  on  an 
indicator  diagram  represents  work  done.  Thus  the  area 
below  the  line  be,  measured  down  to  the  base  line,  represents 
the  work  done  by  the  gases  upon  the  piston  while  expanding. 
Similarly  the  area  below  da  represents  the  work  done  by 
the  piston  on  the  gas  when  it  compressed  the  latter. 

It  is  obvious  that  the  area  under  ed  representing  the 
work  done  by  the  gases  upon  the  piston  during  the  suction 
stroke  is  (in  this  case)  just  equal  to  the  area  under  de,  which 
represents  the  work  done  by  the  piston  on  the  gas  during 
the  exhaust  stroke.  It  therefore  follows  that  the  net 
quantity  of  work  obtained  as  a  result  of  all  four  strokes  will 
be  the  difference  between  the  work  done  by  the  gases  upon 
the  piston  during  the  expansion  stroke  and  the  work  done 
by  the  piston  on  the  gases  during  the  compression  stroke. 
But,  considering  areas  on  the  diagram,  this  net  work  is 
represented  by  the  area  abcda  which  is  hatched. 

Thus,  although  four  strokes  are  necessary  to  complete 
the  practical  cycle,  the  area  under  line  ed  cancels  that  under 
de,  leaving  the  net  work  as  the  net  result  of  the  other  two 
strokes.  The  two  strokes  ed  and  de  are,  however,  necessary, 
the  first  being  used  to  introduce  the  new  charge  and  the 
second  to  expel  the  burned  charge.  They  are  for  these 
reasons  called  pumping  strokes.  They  are  necessitated 
by  practical  considerations  and  must  always  exist  in  some 
form  in  all  real  engines. 


38  GAS  POWER 

The  thermal  efficiency  of  the  ideal  Otto  cycle,  that  is, 
the  ratio  of  the  net  work  to  the  heat  supplied  for  obtaining 
that  work,  is  given  by  the  formula 

Efficiency  =  l~*r (3) 

•*  a 

in  which 

Ta  =  absolute  temperature  at  the  beginning  of  com- 
pression, and 
Ta  —  absolute  temperature  at  the  end  of  compression. 

Since  the  temperature  at  the  end  of  compression  will 
increase  with  the  final  pressure  if  the  initial  conditions 
remain  the  same,  it  follows  that,  with  a  given  initial  pres- 
sure, the  efficiency  of  the  cycle  will  be  greater  the  higher 
the  compression  pressure,  that  is,  the  smaller  the  clearance 
volume.  This  fact  is  of  great  importance  and  should  be 
remembered. 

30.  Actual  Indicator  Card  for  Four-stroke  Operation. 
In  Fig.  10  is  shown  a  typical  indicator  card  for  the  four- 
stroke  Otto  cycle,  except  that  the  lower  loop  of  the  diagram 
has  been  exaggerated  in  size,  for  purposes  of  explanation. 
The  actual  card  has  been  superimposed  upon  an  ideal 
card  in  order  to  accentuate  the  variations. 

Referring  now  to  Fig.  10,  assume  the  piston  to  be  at 
e',  the  end  of  the  stroke,  with  the  clearance  space  filled 
with  burned  gases  at  a  pressure  slightly  above  atmospheric 
due  to  the  frictional  resistance  offered  by  the  exhaust  ports 
and  passages  to  the  burned  gases  which  have  been  expelled 
along  the  line  d'e'.  As  the  piston  moves  outward  on  its 
suction  stroke,  the  clearance  gases  expand  along  e'jf  to 
some  pressure  /  below  atmospheric  before  the  new  charge 
begins  to  flow  through  the  open  valve  into  the  cylinder. 
This  flow  continues  to  g,  forming  the  suction  line  fg,  and  the 
cylinder  is  filled  with  a  mixture  of  new  charge  and  burned 
gas  left  from  the  preceding  cycle.  The  piston  now  returns 


V.     FOUR-  AND  TWO-STROKE  OPERATION 


39 


and  compresses  the  charge  along  the  line  gaf,  to  the  point 
a',  where  ignition  occurs  and  the  combustion  line  a'b'  is 
produced. 

Owing  to  the  fact  that  the  piston  does  not  remain 
stationary  at  a' ',  and  also  because  combustion  is  not  instan- 
taneous throughout  the  entire  mass  of  mixture,  the  line 
a'b'  is  not  vertical  but,  with  proper  setting  of  the  spark  and 
a  correct  mixture,  slopes  slightly  to  the  right. 


-ft^-^f/  Atmog. 


FIG.  10. — Modifications  of  Ideal  Otto  Diagram. 


The  gases  now  expand  behind  the  piston  on  the  third 
stroke,  until  the  point  c'  is  reached,  at  about  85  to  90  per 
cent  of  the  out-stroke,  where  the  exhaust  valve  must  start 
to  open  in  order  to  be  fully  opened  before  the  end  of  the 
stroke  is  reached  and  to  allow  the  greater  part  of  the  charge 
to  escape  before  the  return  stroke  starts.  The  point  d' 
is  slightly  above  atmospheric  pressure,  because  as  the  pis- 
ton returns  on  its  fourth  stroke,  the  passages  and  parts 
offer  a  slight  resistance  to  the  gases,  thus  necessitating  a 


40  GAS  POWER 

pressure  greater  than  atmospheric  to  cause  flow.  The 
Velocity  of  the  gases  through  the  exhaust  port  varies  from 
80  to  125  feet  or  more  per  second,  and  to  produce  this,  the 
exhaust  pressure  line  must  be  from  one  to  three  pounds 
above  atmospheric. 

The  area  of  the  "  lower-loop,"  represents  the  work 
(force  X  distance)  done  upon  the  gas  by  the  piston  and 
consequently  must  be  subtracted  from  the  total  positive 
work  (or  the  area  of  the  upper  loop  of  the  card)  in  order  to 
obtain  the  net  useful  work  of  the  engine.  The  lower  loop 
area,  however,  is  so  small  on  an  actual  card  that  it  is  usually 
neglected,  in  determining  the  I.H.P.  (indicated  horse- 
power) of  a  real  engine. 

31.  Practical  Modifications  of  Four-stroke  Diagram. 
In  Fig.  11  is  given  the  perfect  diagram  of  Fig.  10  with  cards, 
such  as  might  be  obtained  from  practice,  superimposed 
on  it  to  show  the  discrepancies  often  existing  between  the 
actual  and  the  ideal. 

In  an  actual  engine  it  is  found  that,  for  best  operation, 
ignition  of  the  compressed  charge  should  occur  before  the 
piston  has  reached  the  end  of  its  stroke,  as  at  m  in  the 
figure,  because  combustion  does  not  occur  instantaneously. 
With  a  proper  mixture  and  correct  setting  of  the  spark,  a 
combustion  line  such  as  afbf  will  result,  which  is  practi- 
cally a  vertical  line  or  is  slightly  inclined  to  the  right,  thus 
approximating  the  constant  volume  line  of  the  theoretical 
cycle.  If  the  spark  is  too  early,  the  line  nri  will  result, 
while  a  late  setting  of  the  spark  will  give  combustion  lines 
like  a'  b",  a'  b'",  a'  b"",  etc. 

Due  to  imperfect  or  slow  burning  of  the  charge,  many 
cards  have  a  rounded  top,  expansion  beginning  after  the 
piston  has  already  passed  over  an  appreciable  distance 
on  its  return  stroke.  Also,  it  will  be  found  that  in  practice 
there  is  an  actual  transfer  of  heat  to  and  from  the  cylinder 
walls  during  the  various  events,  so  that  the  expansion  and 
compression  curves  do  not  coincide  with  the  corresponding 


V.     FOUR-  AND  TWO-STROKE  OPERATION 


41 


curves  of  the  ideal  cycle.  This  means  that  the  curves 
follow  some  law  expressed  by  the  equation  PVn  =  constant 
instead  of  the  law  PVy  =  constant,  which  is  the  law  of 
the  adiabatic  change.  For  a  detailed  discussion  of  these 
laws  of  gases,  refer  to  any  good  text-book  on  Thermody- 
namics. 

In  theory  it  is  assumed  that  ignition  is  perfect,  that  the 
composition  of  the  charge  is  uniform,  and  that  combustion 
is  complete  and  perfect.  None  of  these  things,  however, 
obtain  in  practice,  and  all  the  variations  have  their  influence 
upon  the  engine  performance. 


FIG.  11. — Modifications  of  Ideal  Otto  Diagram. 

Numerous  other  changes  may  be  made  in  the  diagrams 
obtained  from  real  engines  by  improper  setting  of  valves, 
leaky  pistons,  and  many  other  things.  These  will  be  dis- 
cussed in  a  later  chapter. 

32.  Two-stroke  Operation,  Otto  Cycle.  The  chief 
difference  between  four-  and  two-stroke  operation  is  in  the 
method  of  charging  the  cylinder  and  then  exhausting  the 
burned  gases.  The  other  events  are  practically  the  same 
in  both  types.  This  difference  results  from  the  fact  that 


42 


GAS  POWER 


the  two-stroke  engine  uses  a  charging  pump  to  do  the  pump- 
ing work  done  by  the  engine  piston  in  four-stroke  operation. 

In  Fig.  12  is  shown  a  diagrammatic  representation  of 
the  two-stroke  egine. 

The  pump  cylinder,  which  is  represented  as  being 
entirely  separate  from  the  power  cylinder,  has  an  admission 
valve,  A,  and  a  discharge  valve,  7,  the  latter  also  acting 
as  an  inlet  valve  to  the  power  cylinder.  This  cylinder  has 
a  ring  of  ports,  E,  cut  through  the  walls  at  such  a  point 


To  Atmosphere 


FIG.  12. — Idealized  Two-stroke  Otto  Engine. 

that  the  piston,  by  uncovering  them  near  the  end  of  its 
stroke,  acts  as  an  exhaust  valve.  » 

Now  consider  the  power  cylinder  rilled  with  mixture 
at  atmospheric  pressure  d,  Fig.  12a,  the  piston  just  cover- 
ing ports  E.  The  first  stroke  is  to  the  left,  causing  com- 
pression of  the  charge  along  the  line  da.  Combustion 
produces  the  line  ab,  followed  by  the  expansion  line  be. 
At  c  the  ports  are  uncovered,  allowing  exhaust  to  occur 
along  a  sloping  exhaust  line  cc'.  We  now  assume  that 
the  power  piston  moves  from  c'  to  d  while  the  auxiliary 
pump,  which  has  already  drawn  in  a  charge  of  mixture 


V.     FOUR-  AND  TWO-STROKE  OPERATION          43 

through  valve  A,  forces  it  into  the  power  cylinder  through 
valve  I.  This  new  charge  is  supposed  to  push  the  burnt 
gases  ahead  of  it  and  out  through  the  ports  E,  and  the  piston 
is  operated  to  close  these  ports  just  as  the  new  mixture 
reaches  them.  Conditions  are  now  the  same  as  at  the 
beginning  and  the  cycle  is  repeated. 

Line  ef,  Fig.  12(6)  is  the  line  formed  in  the  pump  cylin- 
der (ideal  case)  when  the  charge  is  drawn  in  at  atmospheric 
pressure.  Line  fe  is  the  line  formed  when  the  charge  is 
forced  into  the  power  cylinder  under  the  same  conditions. 
These  coincide  in  the  ideal  case  and  therefore  cancel, 
leaving  the  area  abc  c'd  as  the  net  area  of  the  power  diagram, 
which  is  practically  the  same  as  in  the  four-stroke  operation 
already  described.  Theoretically,  by  making  the  ports 
of  zero  length,  or  by  using  an  auxiliary  exhaust  valve, 
such  as  a  sleeve,  outside  the  ports,  the  two-stroke  diagram 
could  have  been  made  identical  with  that  of  the  four- 
stroke  operation.  The  principal  difference  in  the  two 
methods  of  operation  is  that  the  pumping  strokes  ef  and 
fe  are  accomplished  outside  the  power  cylinder  in  two-stroke 
operation  while  in  the  four-stroke  engine,  the  power  cylinder 
itself  does  the  pumping. 

The  operations  as  ordinarily  carried  out  are  shown 
in  Fig.  13,  where  the  heavy  lines  represent  an  actual  two- 
stroke  card.  The  exhaust  port  opens  at  a  and  part  of  the 
exhaust  gases  escape.  Scavenging  (cleaning  the  cylinder  of 
burned  gases)  begins  about  6;  charging  commences  between 
6  and  c  and  continues  to  some  point  d,  where  compression 
begins.  There  are  some  modifications  of  this,  but  these 
are  special  cases. 

It  is  obvious,  therefore,  that  the  exhaust,  scavenging 
and  charging  operations,  must  be  accomplished  while  the 
piston  is  moving  from  a  to  c  and  back  to  d  or,  roughly, 
during  about  10  per  cent  of  the  stroke.  This  gives  a  very 
short  time  for  these  important  operations  and  the  difficulty 
of  preventing  the  mixing  of  burned  gases  and  fresh  charge, 


44 


GAS  POWER 


and  of  precluding  the  loss  of  combustible  mixture  through 
the  exhaust  openings  is  very  great.  With  high-speed  engines 
conditions  are  naturally  worse. 

After  the  admission  port  is  closed  at  dt  the  charge 
is  compressed  to  e,  where  it  is  ignited  and  burned.  The 
intrinsic  energy  of  this  high-pressure  gas  now  causes  expan- 
sion on  the  second  stroke  down  to  point  a,  after  which  the 
cycle  is  repeated. 

It  will  be  noted,  therefore,  that  the  more  perfect  the 
scavenging  of  the  cylinder  of  burned  gases,  the  better  will 


FIG.  13. — Actual  Two-stroke  Diagram. 


be  the  operation  of  a  two-stroke  engine.  This  must  be 
accomplished  in  a  very  short  period  of  time,  as  shown  above, 
requiring  an  exhaust  port  of  ample  size.  The  quantity 
of  the  new  charge,  and  its  combustibility,  are  directly 
dependent  on  the  throughness  of  the  scavenging  operation. 
By  the  time  point  c  is  reached,  the  exhaust  gases  should 
be  at  approximately  atmospheric  pressure,  since  the  volume 
of  the  gases  remaining  in  the  cylinder  as  well  as  the  work 
done  in  displacing  them  is  thus  reduced.  For  this  reason 
an  exhaust  valve  is  generally  eliminated  and  a  ring  of  ports, 
uncovered  each  stroke  by  the  piston,  is  used  instead. 


V.     FOUR-  AND  TWO-STROKE  OPERATION 


45 


The  two  agents  used  for  scavenging  are  pure  air  and  fuel 
mixture,  and  these  are  furnished  in  three  ways,  viz: 

(1)  By  independent  pumps,  Fig.  14  (a). 

(2)  By  designing  some  part  of  the  engine,  as  one  end  of 
a  cylinder  or  the  barrel  holding  the  crosshead  guides,  to 
act  as  a  pump,  Fig.  14,  (6),  (c)  and  (d). 


Power  Cylinder 


.Pump  Cylinder 


FIG.  14(a). 


Power  Cylinder 


Pump  Cylinder 

FIG.  14(6). 


(3)  By  using  the  crank  case  and  the  front  side  of  the 
piston,  Fig.  14  (e). 

It  has  been  found  that  the  scavenging  agent  should 
be  at  a  low  and,  if  possible,  a  constant  pressure,  which 
will  prevent  the  incoming  air  from  bursting  through  the 


46 


GAS   POWER 


FIG.  14(c). 


FIG.  14(d). 


_    -J-  Power 
Cylinder 


FIG.  14(e), 


V.      FOUR-  AND  TWO-STROKE  OPERATION 


47 


burned  gases  and  breaking  them  up,  but  will  cause  it  to  act 
as  a  more  or  less  solid  wall  pushing  the  exhaust  gases  out 
ahead  of  it. 

In  nearly  all  of  the  small  two-stroke  engines  the  crank 
case  is  used  as  a  pump  for  the  fresh  charge,  raising  the 
pressure  to  6  or  8  pounds  above  atmospheric  on  the  out 
stroke  of  the  piston.  This  pressure  is  just  enough  to  force 
the  gases  through  the  passages  and  into  the  cylinder  the 
moment  the  admission  port  is  uncovered  by  the  piston. 
This  method,  however,  is  not  used  in  large  engines,  but 
instead,  separate  pumps  for  the  air  and  gas  are  installed 
directly  on  the  frame,  and  outside  the  cylinder  proper. 


FIG.  15. — Pump  Diagram;  Two-cycle  Engine. 


Thus  it  is  clear  that  in  order  to  show  all  the  phases 
passed  through  by  the  charge,  during  each  cycle,  at  least 
two  indicator  diagrams  are  necessary:  one  for  the  power 
cylinder  and  one  for  the  pump,  the  latter  being  part  of 
the  engine  or  separate. 

Referring  to  Fig.  15,  which  shows  a  pump  diagram,  the 
piston  begins  at  c  to  draw  a  fresh  charge  into  the  pump 
cylinder  and  continues  along  the  line  c-d,  which  falls  slightly 
below  atmospheric  pressure  due  to  the  partial  vacuum 
formed.  The  piston  is  now  driven  forward  by  the  explosion 
in  the  power  end  of  the  cylinder,  and  the  mixture  in  the  pump 
cylinder  is  compressed  along  d-a  until  at  a  the  piston  uncovers 
the  inlet  port  of  the  cylinder,  when  the  charge  is  released 


48  GAS  POWER 

on  entering  the  cylinder  along  a-b  and  drops  in  pressure 
to  6.  The  piston  now  returns,  and  the  pressure  in  the  pump 
chamber  drops  rapidly  to  c,  where  the  cylinder  port  is 
covered,  preventing  further  escape  of  the  mixture.  Further 
movement  of  the  piston  causes  a  drop  below  atmospheric 
pressure  when  the  succeeding  card  is  formed. 

33.  Practical  Modification  of  the  Two-stroke  Diagram. 
In  practice,  the  actual  card  would  not  coincide  with  the 
theoretical,  the  maximum  explosion  pressure  being  at  some 
point  /  below  /',  Fig.  13.     The  expansion  and  compression 
lines  as  in  the  four-stroke  diagram  would  also  obey  laws 
other  than  the  ideal. 

34.  Comparison  of  Four-stroke  and  Two-stroke   Oper- 
ation.    It  has  been  shown  that  the  diagrams  of  events  for 
four-stroke  and  two-stroke  operation  are  practically  alike, 
the  modifications  of  the  toe  of  the  'diagram  in  the  latter 
type  being  so  small  as  to  be  negligible.     On  the  basis  of 
the  theoretical  diagrams  there  is  therefore  little,   if  any, 
choice  between  the  two  types.      There  are,  however,  certain 
practical  considerations  which  should  be  noted. 

On  a  basis  of  power  obtained  from  a  given  size  of  cylinder, 
two-stroke  operation  would  seem  to  be  preferable.  In  this 
type  a  complete  cycle  is  obtained  every  revolution,  whereas 
it  takes  two  revolutions  with  the  other  method  to  complete 
a  cycle  and  produce  the  same  amount  of  power  in  the  same 
sized  cylinder.  This  would  indicate  that  a  two-stroke 
engine  should  give  twice  the  power  of  a  four-stroke  engine 
with  the  same  piston  displacement  and  running  at  the  same 
speed. 

Practically,  however,  this  is  not  the  case,  and  the  power 
actually  obtained  varies  from  about  1.3  to  1.7  of  that 
obtained  from  similar  four-stroke  engines.  This  is  due 
to  a  number  of  causes,  but  principally  to  the  difficulty  of 
obtaining  perfect  scavenging  and  a  pure  charge,  so  that  the 
real  two-stroke  diagram  does  not  generally  approximate 
its  ideal  as  closely  as  does  the  four-stroke. 


V.      FOUR-  AND  TWO-STROKE  OPERATION          49 

In  the  better  and  larger  types  of  two-stroke  engines, 
separate  pump  cylinders  are  always  used.  These,  when 
coupled  with  proper  design,  may  be  made  to  give  very 
perfect  scavenging,  but  experience  shows  that  they  then 
entail  friction  losses  of  such  magnitude  as  to  cut  down 
the  useful  work  delivered  by  the  engine,  so  that  the  ideal 
of  double  the  power  of  a  similar  four-stroke  engine  is  never 
realized. 

So  far  as  thermal  efficiency  is  concerned,  theory  would 
indicate  both  methods  of  operation  to  be  equally  desirable. 
Practically,  however,  two-stroke  operation  does  not  give 
as  high  thermal  efficiencies  as  the  other  method.  In  the 
smaller,  simpler  types,  this  is  due  to  the  poor  scavenging 
and  to  the  loss  of  unburned  fuel  through  the  exhaust  ports 
during  scavenging.  In  the  larger  and  more  complicated  types, 
losses  of  this  kind  are  diminished,  but  the  added  friction 
losses,  due  to  the  presence  of  elaborate  pumps,  partly  or 
wholly  counterbalance  the  more  perfect  cylinder  action. 

Many  two-stroke  engines  are  much  more  sensitive  in 
operation  than  similar  four-stroke  machines,  because  of 
the  great  difficulty  experienced  in  exhausting,  scavenging, 
and  charging  in  the  short  time  available.  This  fact  has 
prejudiced  many  against  two-stroke  operation,  but  the  excel- 
lent and  consistent  performance  of  many  engines  operating 
in  this  way  proves  that  such  difficulties  are  not  insurmount- 
able and  that  the  operation  of  such  engines  can  be  made 
just  as  certain  as  that  of  the  other  type. 

It  should  also  be  observed  that  in  designs  in  which  the 
crank  case  or  some  similar  part  of  the  engine  is  used  as  a 
pump,  the  elaborate  cam  shafts  and  valves  of  the  four- 
stroke  engine  may  be  partly  or  wholly  omitted,  and  this 
same  sort  of  simplicity  can  be  more  or  less  incorporated  in 
even  larger  and  more  elaborate  types. 

As  a  result  of  these  and  other  similar  considerations, 
practice  has  been  standardized  in  general  along  the  follow- 
ing lines: 


50  GAS  POWER 


(a)  Where  cheapness,  simplicity,  and  light  weight  for 
a  given  power  are  controlling  factors,  particularly  for  small 
powers,  two-stroke  operation  is  very  extensively  used. 
Thus  a  great  many  of  the  smaller  farm  engines  operate  in 
this  way.  Similarly  small  motor  boat  engines  are  very 
commonly  built  to  operate  on  the  two-stroke  principle. 
For  the  same  reasons,  the  smaller  engines  built  for  opera- 
tion in  the  oil  and  natural  gas  fields  utilize  this  method. 

(6)  On  the  other  hand,  where  great  and  rapid  variations 
of  load  are  expected  and  where  high  thermal  efficiency 
is  desired,  four-stroke  operation  is  generally  given  the 
preference.  Thus  most  automobile  engines  operate  in 
this  way,  although  it  must  be  admitted  that  at  least  one 
two-stroke  engine  has  proven  itself  fully  the  equal  of  the 
more  elaborate  four-stroke  engine  for  this  service.  Again, 
nearly  all  large  engines  use  the  four-stroke  method  because 
of  the  higher  thermal  efficiency  and  the  greater  simplicity 
resulting  from  the  omission  of  separate  pumping  cylinders. 
Here. again,  however,  it  is  worthy  of  note  that  some  of  the 
large  two-stroke  constructions  have  shown  themselves 
fully  the  equal  of  their  more  popular  rivals. 

(c)  There  is  one  field  in  which  the  two-stroke  method 
is  preeminently  successful.  In  all  liquid  fuel  engines  in 
which  the  fuel  is  sprayed  into  the  cylinder  at  the  end  of  the 
compression  stroke,  air  only  (and  not  combustible  mixture) 
is  admitted  to  the  cylinder  and  compressed  therein.  Such 
engines  may,  therefore,  operate  on  the  two-stroke  principle 
without  danger  of  losing  fuel  through  the  exhaust  port  and, 
if  sufficient  scavenging  air  is  available,  almost  complete 
expulsion  of  the  exhaust  gases  is  possible.  For  small  engines 
of  this  type  two-stroke  operation  is  therefore  advisable 
because  the  lack  of  valves  and  the  increased  power  for  a 
given  weight  reduce  initial  cost,  while  the  thermal  efficiency 
is  not  lowered  by  loss  of  fuel  through  the  exhaust  ports. 
For  large  engines  of  this  type,  two-stroke  operation  brings 
the  added  advantage  of  reducing  the  size  of  cylinders 


V.     FOUR-  AND  TWO-STROKE  OPERATION          51 

required  for  a  given  power.  This  is  a  very  important 
consideration,  particularly  in  the  case  of  large  Diesel  engines, 
in  which  the  high  gas  pressures  make  the  successful  con- 
struction and  operation  of  large  cylinders  a  very  difficult 
matter. 

35.  The  Diesel  Engine.  Having  described  in  detail 
the  operation  of  the  four-  and  two-stroke  Otto  cycles,  it  is 
pertinent  at  this  point  to  show  briefly  the  method  of  opera- 
tion of  the  Diesel  engine,  which  is  being  used  so  extensively 
in  Europe  at  the  present  time. 

The  real  Diesel  cycle  may  be  completed  in  two  or  four 
strokes,  and  the  mechanical  operations  within  the  power 
cylinder  are  very  similar  to  those  of  the  Otto  engine. 

In  the  four-stroke  engine,  the  cylinder  is  charged  with 
air  during  the  suction  stroke,  and  this  is  compressed  on  the 
return  stroke  into  a  very  small  clearance  volume,  resulting 
in  a  very  high  terminal  pressure  of  500  pounds  per  square 
inch  or  more.  The  corresponding  temperature  is  also  very 
high,  in  fact  it  reaches  such  a  point  that  it  will  ignite  liquid 
fuel  injected  into  it  in  a  fine  spray.  At  about  the  end  of 
the  compression  stroke,  a  small  quantity  of  finely  atomized 
liquid  fuel  is  blown  into  the  clearance  space  by  means  of  an 
air  blast,  at  a  pressure  of  about  100  to  500  pounds  above 
the  compression  pressure  in  the  cylinder.  This  high 
pressure  air-blast  carries  the  completely  atomized  particles 
into  the  highly  compressed  and  heated  air  in  the  cylinder, 
where  they  are  immediately  vaporized  and  ignited.  Injec- 
tion continues  during  the  first  part  of  the  stroke  of  the 
piston,  ceasing  at  about  10  per  cent  of  stroke  at  rated  load. 
Thus  combustion  is  effected  without  pressure  rise,  the  fuel 
being  admitted  and  burned  at  such  a  rate  as  to  maintain 
almost  a  constant  pressure  during  the  first  part  of  the  out- 
stroke. 

In  Fig.  16  are  shown  an  ideal  and  a  real  Diesel  four- 
stroke  card  superimposed,  with  the  lower  loop  slightly 
exaggerated. 


52 


GAS  POWER 


to 


The  thermal  efficiency,  which   for   any   engine  is    equal 

Heat    converted   into  mechanical   energy 

— ,  is  especially 


Total  heat  supplied 
high  in  the  Diesel  engine,  running  to  30  or  32  per  cent  or 
more,  measured  at  the  brake.  The  Diesel  motor  has  found 
very  wide  application  abroad  both  in  stationary  and  marine 


it- 


Displacement 


FIG.  16.— Diesel  Cards. 


practice.  Because  of  the  method  employed  in  compress- 
ing the  air  alone  to  a  high  temperature  and  pressure,  it 
lends  itself  readily  to  the  use  of  liquid  fuels,  and  it  will 
readily  handle  many  of  the  heavier  petroleum  oils  and  a 
number  of  by-product  tars. 


CHAPTER  VI. 
METHODS  OF  COOLING. 

36.  Necessity  of  Cooling.  It  will  be  shown  in  a  later 
chapter  that  practically  all  internal  combustion  engines 
must  be  supplied  with  from  7500  to  14,000  B.t.u.  per 
effective,  or  shaft,  horse-power  per  hour.  Of  this  the 
greater  part  is  actually  liberated  by  combustion  in  the 
cylinder,  but  only  about  25  to  35  per  cent  is  converted 
into  useful  work.  The  remainder,  being  energy  and  there- 
fore indestructible,  must  be  dissipated  in  other  ways.  It 
is  lost  in  three  ways:  (a)  part  passes  off  in  the  hot  exhaust 
gases  expelled  from  the  cylinder;  (6)  part  is  lost  by  friction 
in  the  mechanism,  heating  the  moving  parts  and  being- 
radiated  into  space;  and  (c)  the  rest  is  carried  off  by  some 
cooling  medium.  Unless  this  were  done  the  cylinder  and 
connected  parts  would  ultimately  attain  a  very  high  tem- 
perature and  would  then  radiate  heat  rapidly  enough  to  main- 
tain a  balance  between  supply  and  waste  unless  the  engine 
ceased  operation  because  of  mechanical  difficulties  before 
this  condition  was  reached.  To  prevent  this  overheating, 
which  would  preclude  satisfactory  lubrication  and  mechani- 
cal operation,  all  internal  combustion  engines  are  artificially 
cooled  m  some  way. 

In  the  smaller  engines,  only  the  cylinder  or  the  cylinder 
and  the  cylinder  head  need  be  cooled,  but  in  the  largest 
double-acting  types,  it  is  customary  to  cool  the  cylinders, 
cylinder  heads,  exhaust  valves,  pistons,  and  piston  rods. 

In  general,  from  25  to  40  per  cent  of  all  the  heat  supplied 
the  engine  is  dissipated  by  this  artificial  cooling.  Assuming 

53 


54 


GAS   POWER 


that  the  average  engine  requires  about  10,000  B.t.u.  per 
effective  horse-power  hour,,  and  that  30  per  cent  of  this  is 
carried  away  by  cooling,  we  have  about  3000  B.t.u.  per 
horse-power  hour,  to  dispose  of.  In  a  1000  h.p.  engine, 
this  would  be  3,000,000  B.t.u.  per  hour,  or  about  10  per 
cent  more  than  the  amount  converted  into  useful  power, 
and  the  equivalent  of  about  90  boiler  horse-power.  This 
will  give  an  idea  of  the  enormous  waste  which  occurs  in 
this  way. 

37.  Methods  of  Cooling.  The  methods  in  use  for 
cooling  internal  combustion  engines  are  divisible  into  two 
general  classes  which  may  be  called:  (1)  Air  cooling,  and 
(2)  Liquid  cooling.  These  will  be  separately  considered 
in  the  succeeding  paragraphs. 

Air  Cooling  is  effected,  as  the  name  suggests,  by  a  stream 
of  air  which  passes  over  the  surfaces  to  be  cooled.  When 
an  engine  is  to  be  cooled  in  this  way,  the  cylinder  and 
cylinder  head  are  generally  cast  with  webs  as  shown  in 
Fig.  17,  or  have  similar  webs  shrunk  on.  The  circulation 
of  air  may  be:  (1)  natural,  that  is  simply  due  to  the  rising 
of  the  heated  air  which  is  in  contact  with  the  engine  and 
its  replacement  by  air  from  the  surrounding  atmosphere; 
or  (2)  it  may  be  forced  by  the  use  of  a  fan  or  similar  blower, 
driven  from  the  engine,  as  shown  in  the  figure. 

The  forced  circulation  is  preferable  in  all  but  the  very 
smallest  units,  because  it  has  been  found  by  experience 
that  if  natural  circulation  is  depended  on,  the  cylinder 
will  under  some  circumstances  attain  a  higher  temperature 
than  is  consistent  with  good  lubrication  and  satisfactory 
operation.  Natural  circulation  is,  therefore,  seldom  used 
on  engines  developing  more  than  about  two  or  three  horse- 
power and  generally  only  on  still  smaller  sizes. 

Theoretically  there  is  no  limit  to  the  size  of  engine  which 
can  be  satisfactorily  cooled  by  forced  circulation  of  air,  as 
it  is  merely  a  question  of  circulating  enough  air  at  a  high 
enough  velocity  to  remove  the  necessary  amount  of  heat. 


VI.     METHODS  OF  COOLING 


55 


Practically,  however,  there  is  a  commercial  limit,  set  by  the 
cost  of  the "  pumping  mechanism  and  its  operation,  beyond 
which  it  does  not  pay  to  go  under  any  given  circumstances. 
Thus  few  stationary  engines  larger  than  5  h.p,  are  built 
for  air-cooling  even  with  forced  circulation,  and  most  of 
them  are  still  smaller. 

One  very  notable  example  of  forced-air  circulation  is 
that  used  on  the  Franklin  automobile  engine.  Each  cyl- 
inder of  this  engine  is  capable  of  developing  about  6  h.p., 
and  the  air  cooling  has  proved  satisfactory.  A  very  elab- 
orate sheet-metal  casing  is  used  to  direct  the  air  over  the 


FIG.  17. — Air-cooled  Engine. 


parts  to  be  cooled,  the  circulation  being  maintained  by  a 
well-designed,  high-speed  blower  driven  from  the  engine. 

There  are  several  marked  advantages  of  air  cooling 
in  comparison  with  water  cooling,  which  is  the  most  common 
example  of  liquid  cooling.  The  principal  ones  are: 

1.  No  charge  for  the   cooling  medium,   as  air   is  free 
to  all  and  available  in  all  places. 

2.  No  danger  of  rupture  of  the  engine  cylinder  and  other 
cooled  parts  by  freezing,  as  in  the  case  of  water  cooling  if 
the  jacket  is  not  drained  when  the  engine  stands  idle  in 
freezing  weather. 


56 


GAS   POWER 


3.  No    danger  of  damaging  the  engine  by  forgetting 
to  turn  on  the  supply  of  cooling  medium  when  starting  the 
engine,  as  air  cooling  is  automatic. 

4.  Simplicity,  if  properly  designed. 

5.  Low  cost,  as  the  castings  are  simpler  and  there  are 
no  piping  and  other  auxiliaries  to  pay  for. 

6.  No  necessity  for  cleaning  out  restricted  jacket  spaces 
as  is  the  case  with  water  cooling  when  using  water  carrying 
scale-forming  material  or  mud  in  solution  or  suspension. 

7.  Light  weight. 

To  partially  balance  these  advantages  are  the  following 
disadvantages: 

1.  The  method  is  applicable  only  to  small  sizes. 

2.  There   is   practically   no   positive    control    over   the 
temperature  of  the  engine,  so  that  it  generally  runs  cooler 
than  necessary  in  cold  weather  and  at  too  high  a  temper- 
ature in  warm  weather  or  when  operated  in  restricted  spaces 
which  prevent  the  inflow  of  a  continuous  supply  of  cold  air. 

3.  The  exhaust  is  smoky  in  warm  weather,  due  to  the 
cracking  and  burning  of  the  cylinder  lubricating  oil  in  a 
hot  cylinder. 

4.  Rapid  fouling  of  piston  rings,  piston,  and  combustion 
space  occurs  through  the  deposit  of  carbon  formed  by  the 
cracking  and  partial  combustion  of  the  cylinder  oil. 

Water  Cooling  may  be  called  the  standard  method, 
as  it  is  with  few  exceptions  the  method  used  with  the  better 
engines,  and  is  the  only  method  available  for  use  in  all  but 
the  smallest  sizes.  Oil  cooling  has  been  used  on  some 
engines,  but  has  not  found  extensive  application.  As  with 
air  cooling,  there  are  two  distinctly  different  methods  of 
water  cooling  in  use,  namely:  natural  circulation,  depend- 
ing on  the  density  changes  accompanying  temperature 
changes,  and  forced  circulation,  depending  on  a  natural 
or  artificially  created  head  of  water. 

Natural  Circulation  is  applied  in  two  different  ways: 
one  system  is  known  as  hopper  cooling;  the  other  as  tank 


VI.     METHODS  OF  COOLING 


57 


cooling.  A  hopper-cooled  engine  is  shown  in  Fig.  18.  As 
the  water  is  heated  by  contact  with  the  hot  walls  of  the 
cylinder  it  is  forced  upward  and  its  place  is  taken  by  cooler 
water  descending  from  the  hopper  as  shown.  Naturally, 
the  isolated  body  of  water  contained  in  the  jacket  and 
hopper  tends  to  attain  higher  and  higher  temperatures  as 
it  is  supplied  with  heat.  This  tendency  is  more  or  less 
balanced  by  the  lowering  of  temperature  by  the  radiation 
of  heat  from  the  exterior  of  the  jacket  and  hopper;  by 
conduction  to  and  radiation  from  the  other  parts  of  the 


(a)  SECTION  ON  A-B  SHOWING 
CIRCULATION 


(b)    SECTIONAL  ELEVATION 


Inlet 

(C)    SECTION  ONC-D 


FIG.  18. — Hopper-cooled  Engine. 


engine;  and  by  vaporization  from  the  exposed  surface  of 
water  in  the  hopper. 

In  any  case,  a  very  definite  limit  to  the  maximum  tem- 
perature attainable  is  naturally  set.  The  water  cannot 
be  raised  to  a  temperature  higher  than  boiling  temperature 
at  atmospheric  pressure,  so  that,  as  long  as  the  jacket  and 
hopper  contain  water,  the  temperature  is  limited  to  about 
212°  F.  For  small  engines  and  even  for  engines  develop- 
ing 25  h.p.,  such  a  temperature  is  permissible  though  not 
desirable. 

Hopper  cooling  has  several  advantages  over  other  types  of 
water  cooling;  the  principal  ones  are: 


58 


GAS  POWER 


1.  Cheapness   in   first    cost    because   of    simplicity    of 
arrangement. 

2.  Cheapness  in  operation    because  the   water  is  prac- 
tically used  up  (evaporated)  instead  of  being  run  through  the 
jacket  and  allowed  to  run  to  waste  as  in  most  forced  water 
circulating  systems. 

3.  Safety  against  damage  by  freezing  because  of  the 
free  expansion  possible  in  the  hopper. 

4.  Light   weight    when   used    with    a   portable    engine 
because  the  amount  of  water  which  must  be   carried  is 
reduced  to  a  minimum. 


FIG.  19. — Tank-cooled  Engine. 


The  principal  disadvantages  are: 

1.  Inability  to  control  the  temperature  of  the  engine, 
as  it  runs  cool  when  carrying  a  light  load  and  runs  hot 
when  carrying  a  heavy  load. 

2.  Danger    of    damage   to   the    engine   through   failure 
to  replace  the  water  which  has  evaporated  from  the  hopper. 

Tank  Cooling  is  shown  in  Fig.  19,  in  which  the  natural 
circulation  is  shown  by  arrows.  This  method  is  older  than 
hopper  cooling  and  is  now  being  largely  replaced  by  the 
latter,  particularly  for  portable  work.  It  is  possible  to 
maintain  a  more  even  temperature  by  using  a  large  tank 


VI.     METHODS  OF  COOLING 


59 


to  facilitate  cooling  and  large  diameter  of  pipes  to  facilitate 
circulation;  but  with  tanks  and  pipes  as  ordinarily  supplied, 
the  method  has  little  advantage  over  the  simpler  hopper. 
A  method  of  tank  cooling  with  forced  circulation  is  shown 
in  Fig.  20,  where  the  water  flows  over  a  conical  screen  before 
entering  the  tank. 

Forced  Water  Circulation  is  used  on  all  large  engines 
and  on  many  of  the  smaller  sizes  when  intended  for  sta- 
tionary work.  An  example  illustrating  its  application  to 
an  ordinary  type  of  horizontal  engine  is  shown  in  Fig.  21. 


FIG.  20. — Cooling  Tower,  witK  Screen  for  Cooling  Water. 

When  this  method  of  cooling  is  used,  it  is  customary 
to  control  the  flow  of  water  so  as  to  maintain  any  desired 
temperature.  Thus  with  small  and  medium-sized  engines, 
the  discharged  water  is  generally  maintained  at  a  temper- 
ature of  about  160°  F.,  while  on  larger  engines,  temperatures 
between  125°  and  140°  are  more  common.  With  large, 
double-acting  engines,  the  cylinder,  cylinder  head,  exhaust 
valve,  and  the  piston  systems  are  generally  each  on  a  sepa- 
rate line — that  is  have  independent  supply  and  discharge — 
and  it  is  customary  to  determine  the  best  temperature  for 
each  system  by  actual  operating  results. 


60 


GAS  POWER 


The  piping  system  for  forced  circulation  should  have  a 
shut-off  valve  on  the  pressure  side  of  the  engine,  a  throttle 
valve  on  the  discharge  side  for  controlling  the  flow,  and  a 
drain  valve  at  the  lowest  point  of  the  system  for  draining 
when  the  engine  is  standing  idle  in  freezing  weather.  This 
is  illustrated  in  Fig.  21.  It  is  very  important  to  note  that 
the  discharge  pipe  must  connect  to  the  highest  point  of  the 
jacket  space  in  order  that  any  air  liberated  as  the  water 
is  heated  may  pass  out  of  the  system  and  not  remain  caught 
in  a  pocket,  thus  eventually  causing  local  overheating. 


Water  Outs 


FIG.  21. — Forced  Water  Circulations,  Showing  External  Piping  System. 


All  water-jacketed  engines  should  be  so  arranged  that 
the  jacket  space  can  easily  be  cleaned  out.  This  is  necessary 
because  mud  and  various  salts  are  deposited  in  this  space 
just  as  they  are  in  a  steam  boiler,  and,  with  bad  water, 
it  does  not  take  long  to  seriously  decrease  the  effectiveness 
of  the  jacket.  It  is  not  at  all  uncommon  to  find  engines 
in  which  the  jacket  space  is  almost  entirely  filled  with 
scale  and  mud,  and  many  failures  have  been  due  to  this 
cause.  Cleaning  is  generally  provided  for  by  means  of 
hand  holes  which  are  closed  with  cover  plates  during 
operation. 


VI.     METHODS  OF  COOLING  61 

38.  Reclamation  of  Cooling  Water.  It  is  not  generally 
realized  that  the  amount  of  cooling  water  required  by  a 
gas  plant  is  a  relatively  large  quantity.  To  obtain  an 
idea  of  the  amount  required,  consider  a  1000  h.p.  engine 
receiving  water  at  a  temperature  of  60°  F.  and  discharging 
it  at  130°  F.  Every  pound  of  water  circulated  will  then 
absorb  about  70  B.t.u.  The  engine  will  probably  require 
about  10,000  B.t.u.  per  horse-power  hour,  and  at  least 
25  per  cent  of  this  will  have  to  be  carried  away  by  the  jacket. 
The  jacket  must  then  remove  about  2500  B.t.u.  per  brake 
horse-power  hour  which  will  require  about  2500-^-70  = 
about  35+  pounds  of  water  per  brake  horse-power  hour. 
When  it  is  remembered  that  an  ordinary  steam  plant  of 
this  size  running  non-condensing  can  deliver  a  brake  horse- 
power hour  on  less  than  this  amount  of  steam  the  importance 
of  the  cooling  water  consumption  becomes  apparent.  For 
the  purpose  of  having  an  ample  supply  to  meet  contingencies 
it  is  common  practice  to  assume  that  a  gas  engine  will  require 
from  4.5  to  9  gallons  of  water  per  brake  horse-power  hour, 
depending  on  the  type,  fuel  used,  etc.  This  corresponds 
to  from  37.6  Ibs.  to  75.2  Ibs.  per  brake  horse-power  hour. 

It  sometimes  happens  that  cooling  water  is  available  at 
a  negligibly  small  cost,  but  this  is  seldom  the  case.  In 
general  it  must  be  pumped  or  purchased,  and  in  either 
event  its  cost  must  be  charged  against  the  power  generated. 
To  keep  down  the  cost  to  the  lowest  possible  figure,  it  is 
customary  in  many  large  plants  to  cool  the  water  coming 
from  the  jackets  so  that  it  can  be  used  over  and  over  again. 
This  cooling  is  generally  effected  by  a  combination  of  radia- 
tion and  evaporation. 

In  the  simplest  plan  for  cooling  the  water  so  that  ii 
may  be  used  again,  the  water  is  run  through  exposed  pipes 
to  an  open  pond  or  tank.  Some  cooling  occurs  by  radia- 
tion from  the  pipes  and  the  rest  is  due  to  radiation  and 
evaporation  from  the  exposed  surface  of  the  tank  or  pond. 
This  simple  method  is  not  applicable  to  very  large  stations, 


62  GAS  POWER 

as  the  exposed  surface  would  have  to  be  prohibitively 
extensive  in  order  to  cool  the  required  quantity  of  water. 

For  larger  installations,  some  method  of  exposing  a 
greater  surface  without  using  too  much  ground  area  must 
be  devised.  There  are  practically  two  methods  in  use> 
In  one,  the  water  is  sprayed  over  a  pond  from  a  great  num- 
ber of  small  nozzles.  Part  of  it  evaporates,  cooling  the 
remainder,  which  falls  and  collects  in  the  pond.  The  latter 
serves  principally  as  a  storage  reservoir.  In  the  other 
method,  some  form  of  cooling  tower  such  as  is  used  for 
cooling  condensing  water  in  steam  plants  is  utilized. 

In  some  small  portable  plants  a  modified  and  diminutive 
form  of  cooling  tower  is  used.  One  variety  is  shown  in  Fig. 
20.  This  arrangement  gives  all  the  advantages  of  tank 
cooling  and  has  the  further  advantages  that  the  cooling 
can  be  made  more  effective  and  that  a  smaller  weight  of 
water  need  be  carried  with  the  plant. 

All  these  methods  result  in  a  constant  loss  of  water  by 
evaporation  and  by  windage.  This  amount  will  vary 
between  about  2  and  10  per  cent,  depending  upon  the 
highest  temperature  attained  by  the  water,  the  condition 
of  the  atmosphere,  the  strength  of  the  wind,  etc.  Even  in 
the  worst  cases,  however,  it  is  far  cheaper  to  do  the  necessary 
pumping  and  to  pay  interest  and  depreciation  charges  on 
pumping  and  cooling  equipment  when  the  price  of  water 
is  at  all  high,  as  it  is  in  many  cities. 

There  is  another  incidental  advantage  attained  by  cool- 
ing and  recirculating  the  jacket  water.  It  has  already  been 
shown  that  the  deposition  of  mud  and  scale  in  jackets  is  an 
important  consideration.  When  a  given  supply  of  water 
i§  continuously  circulated  through  the  system  the  deposit 
of  mud  and  similar  material  is  reduced  to  a  minimum,  as 
only  that  brought  in  by  the  make-up  water  (from  2  to  10 
per  cent  of  the  whole)  is  available  for  deposition. 


•      CHAPTER    VII. 
GOVERNING  AND  GOVERNORS. 

39.  Explanation  of  Governing.  When  an  engine  is  in 
normal  operation  there  is  a  balance  between  the  power  it  is 
generating  and  the  power  which  is  being  used.  If  an  engine 
were  to  develop  more  power  within  its  cylinders  than  is 
required  to  overcome  its  own  friction  and  similar  losses 
and  to  do  the  work  called  for  at  its  shaft,  it  would  have  to 
speed  up  to  absorb  the  excess  power.  The  only  limit  to 
this  would  be  final  rupture  under  the  great  stresses  induced. 
Similarly,  if  it  were  to  develop  less  power  than  required, 
its  speed  would  decrease  until  it  ultimately  came  to  rest. 
Maintaining  a  proper  balance  between  power  generation 
and  power  demand  is  called  governing. 

The  function  of  governing  may  be  further  complicated 
by  the  addition  of  other  requirements  as  well  as  the  main- 
tenance of  a  balance  between  the  power  generated  and  the 
power  demanded.  Thus  it  may  be  necessary  to  be  able  to 
operate  at  various  speeds  while  maintaining  the  above 
balance,  as  with  automobile  and  motor-boat  engines.  In 
every  case,  however,  the  problem  of  governing,  in  the  last 
analysis,  is  the  maintaining  of  this  balance  between  supply 
and  demand.  In  most  stationary  engines  it  is  desirable 
to  maintain  an  approximately  constant  speed  of  rotation 
no  matter  what  the  power  demand.  Thus  if  the  engine 
drives  the  line  shafting  of  a  mill  or  shop,  it  is  generally 
desirable  to  have  that  shafting  run  at  about  the  same 
speed  no  matter  how  much  power  is  being  taken  from  it; 

63 


64  GAS   POWER 

or,  if  the  engine  drives  an  electric  generator,  the  speed 
of  rotation  must  generally  be  approximately  the  same  at 
all  loads. 

This  demand  for  practically  constant  speed  is  so  com- 
mon that  most  people  are  apt  to  think  of  the  governing 
problem  as  that  of  maintaining  a  constant  speed.  To 
show  the  fallacy  of  this,  it  may  be, well  to  cite  a  few  examples 
in  which  this  is  not  the  case. 

Assume  a  gas  engine  driving  a  water-works  pump; 
the  quantity  of  water  pumped  varies  practically  as  the 
speed  at  which  the  *pump  is  operated.  In  most  water 
works,  the  demand  for  water  is  very  variable,  and  therefore 
the  pump  must  be  operated  at  different  speeds  to  meet 
this  variable  demand.  At  each  speed,  the  governor  has  to 
regulate  the  power  output  of  the  engine  to  the  power 
demand  of  the  pump;  the  variable  speed  is  merely  an 
added  requirement. 

The  case  of  an  air  compressor  is  similar.  Many  air 
compressors  vary  their  speed  to  suit  the  demand  for  air, 
and  the  engine  must,  of  course,  do  likewise.  The  automobile 
engine  and  the  motor  boat  engine  have  already  been  cited 
as  examples  of  variable  speed  requirements. 

This  balance  between  supply  and  demand  may  be 
maintained  manually,  as  in  the  automobile  and  marine 
engine;  or  it  may  be  maintained  automatically  by  appropriate 
mechanism,  as  in  the  ordinary  power  engine;  or  it  may  be 
maintained  by  a  combination  of  these  two  methods,  as  is 
often  the  case  with  pumping  engines  in  which  the  mechanism 
is  set  by  hand  for  a  certain  speed  and  then  maintains  the 
required  power  balance  to  preserve  this  speed  until 
again  adjusted  by  hand  for  another  set  of  conditions. 

40.  Methods  Available.  The  power  made  available  in 
an  engine  cylinder  is  dependent  directly  upon:  (1)  The 
net  work  supplied  to  the  piston  by  the  working  substance 
per  cycle,  and  (2)  the  number  of  cycles  performed  per  unit  of 
time.  To  vary  the  power  made  available,  we  may  then 


VII.  GOVERNING  AND  GOVERNORS       65 

vary  the  net  work  supplied  the  piston  per  cycle,  or  we  may 
vary  the  number  of  cycles  per  unit  of  time,  or  we  may  do 
both  in  conjunction.  The  commercial  methods  of  govern- 
ing are  all  based  upon  such  changes. 

41.  Hit  and  Miss  Governing.  One  of  the  commonest 
methods  of  governing  is  called  Hit  and  Miss  governing. 
This  method  operates  on  the  second  possibility  enumerated 
above;  that  is,  it  varies  the  number  of  cycles  per  unit  of 
time.  It  is  generally  used  only  on  engines  which  are  expected 
to  operate  at  about  constant  speed,  and  it  preserves  the 
required  power  balance  by  decreasing  the  number  of  work- 
ing cycles  per  unit  of  time  whenever  the  engine  tends  to  speed 
up  because  of  excess  power  made  available. 

The  name,  hit  and  miss,  is  derived  from  the  type  of 
mechanism  used  to  effect  this  kind  of  governing.  This 
mechanism  is  so  constructed  that  while  the  speed  of  the 
engine  does  not  exceed  the  normal  value  (i.e.,  while  the 
power  being  made  available  does  not  exceed  the  demand) 
some  part  of  the  mechanism  "  hits  "  another  part  neces- 
sary to  produce  a  working  cycle;  when  the  speed  exceeds 
normal,  that  is,  when  the  engine  is  making  available  more 
power  than  is  demanded,  some  part  of  the  mechanism 
"  misses  "  another  part  and  prevents  the  occurrence  of  a 
working  cycle. 

There  are,  in  general,  a  number  of  possible  methods  of 
preventing  the  production  of  a  working  cycle,  i.e.,  causing 
a  "  miss."  Very  few  are,  however,  in  actual  use.  The 
most  common  method  is  to  hold  the  inlet  valve  closed  and 
the  exhaust  valve  open  when  a  "  miss  "  is  desired.  The 
engine  then  merely  pumps  the  burned  gases  from  the 
exhaust  pipe  into  its  cylinder  and  back  into  the  pipe  again 
until  normal  operation  is  resumed  by  allowing  the  valves 
to  function  properly. 

The  control  of  the  valves  is  generally  effected  either  by  a 
pendulum  governor  or  by  a  centrifugal  governor.  Examples 
of  pendulum  governors  are  shown  in  Fig.  22  (a),  (b)  and  (c). 


66 


GAS  POWER 


Examples  of  flyball  governors  as  applied  to  throttling  gov- 
erning, which  will  be  explained  in  a  later  paragraph,  are 
shown  in  Fig.  23,  (a)  and (6). 

The  hit  and  miss  method  of  governing  has  two  marked 
advantages',   they  are: 

1.  It  is  a  comparatively  simple  and  cheap  method,  and 

2.  It  gives  a  high  thermal  efficiency  at  fractional  loads. 
The  latter  point  is  worthy  of  note  both  because  of  its 

practical  bearing  and  because  it  corresponds  with  theoretical 
deductions.  Theoretically  an  internal  combustion  engine 


n 

(6)  (c) 

FIG.  22. — Simple  Forms  of  Pendulum  Governors. 


operating  on  the  Otto  cycle  gives  its  highest  efficiency  when 
producing  approximately  its  maximum  power  cycle. 

It  is  obvious  that  with  hit-and-miss  governing  the  engine 
either  produces  its  maximum  cycle  or  no  cycle  at  all,  and 
hence  all  heat  used  is,  in  theory  at  least,  converted  with 
maximum  efficiency.  In  practice,  the  cooling  of  the  cylinder 
during  missed  cycles,  and  the  disturbance  of  the  fuel,  air 
and  burned  gas  ratios  cause  a  falling  off  in  efficiency  at 
fractional  loads. 

To  counterbalance  the  advantages  enumerated  above, 
this  method  of  governing  is  open  to  the  objection  that 


VII.  GOVERNING  AND  GOVERNORS 


67 


it  is  difficult  to  maintain  as  even  a  speed  as  with  other  methods 
unless  an  excessively  heavy  flywheel  is  used.  This  is  due 
to  the  fact  that  when  in  operation  the  engine  gives  erratically 
distributed  impulses  of  comparatively  great  magnitude 
instead  of  an  evenly  distributed  set  of  impulses  each  grad- 
uated to  suit  the  instantaneous  requirement.  Even  with 
the  other  methods  of  governing,  the  flywheel  must  be  made 
very  heavy  when  close  speed  regulation  is  desired,  so  that 


(a)  Regulating  Butterfly  Throttle. 


(6)   Regulating  Grid  Throttle  Valve.. 


FIG.  23.—  Flyball  Governors. 

hit  and  miss  governing  is  generally  used  only  when  very 
close  regulation  is  not  required. 

42.  Methods  Involving  Variation  of  Cycle.  With  the 
number  of  cycles  per  unit  of  time  remaining  constant, 
the  power  made  available  may  be  varied  by  changing  the 
amount  of  work  done  on  the  piston  per  cycle;  i.e.,  by  changing 
the  work  value  of  a  cycle.  This  can  be  done  in  three  dis- 
tinctly different  ways;  they  are: 

(1)  Changing  the  relative  proportions  of  gas  and  air 
(i.e.,    the    quality    of    the    mixture).     This    is    known    as 
quality  governing. 

(2)  Changing  the  weight  of  constant  quality  mixture 


68  GAS  POWER 

drawn  into  the  cylinder  per  cycle.     This  is  known  as  quan- 
tity governing. 

(3)  Changing  the  time  of  ignition. 

Governing  by  changing  the  time  of  ignition  is  not  desir- 
able because  there  is  a  certain  best  time  of  ignition  for 
each  engine  operating  under  a  given  set  of  conditions. 
When  governing  is  effected  by  changing  the  time,  it  simply 
amounts  to  improper  ignition,  thus  causing  a  loss  of  power 
and  efficiency.  This  method  is,  therefore,  not  tp  be  rec- 
ommended where  economy  and  good  operation  are  desired. 
It  is  often  used  as  a  temporary  means  of  control  in  the  case 
of  automobile  and  small  marine  engines,  and  such  use  is 
justifiable  on  the  grounds  of  convenience  even  though  it 
is  not  efficient. 

Schemes  involving  quality  and  quantity  changes  are 
both  extensively  used  commercially  and  are  the  standard 
methods  of  governing  all  but  the  smaller  and  cheaper 
engines.  They  are  often  called  "  precision  "  forms  of  gov- 
erning in  comparison  with  the  less  precise  hit-and-miss 
method. 

43.  Quality  Governing.  Since  the  internal  combustion 
engine  is  a  heat  engine,  the  quantity  of  work  which  it 
makes  available  in  a  given  time  must,  in  a  general  way, 
be  proportional  to  the  heat  energy  supplied  it;  that  is,  to 
the  quantity  of  fuel  supplied  in  that  time. 

It  follows  from  the  above  that,  if  the  energy  made  avail- 
able is  to  be  decreased,  it  is  only  necessary  to  decrease  the 
quantity  of  fuel  burned  per  cycle;  while  an  increase  in  the 
amount  of  fuel  in  the  mixture  will  cause  an  increase  in  the 
energjr  made  available  provided  sufficient  air  is  present  to 
burn  it  all.  A  series  of  indicator  diagrams  showing  the 
variation  in  size  accompanying  a  variation  in  the  fuel 
supply  is  given  in  Fig.  24.  The  area  of  each  cycle  is,  of 
course,  proportional  to  the  work  done  upon  the  piston 
during  that  cycle,  and  hence  is  a  measure  of  the  energy  made 
available.  The  largest  diagram  corresponds  to  the  rated 


VII.  GOVERNING  AND  GOVERNORS 


69 


load,  with  very  nearly  the  maximum  proportion  of  fuel 
in  the  mixture.  The  smaller  diagrams  correspond  to  smaller 
loads  and  smaller  proportions  of  fuel,  or,  as  it  is  commonly 
expressed,  "  leaner  "  mixtures. 

It  will  be  observed  that  the  compression  pressure  remains 
the  same  for  all  cycles,  indicating  that  a  full  charge  is  drawn 
in  at  all  loads.  Any  diminution  in  the  fuel  charge  is  bal- 
anced by  a  corresponding  increase  in  the  air  charge.  The- 
oretically, this  is  advantageous,  as  the  efficiency  of  the 


Displacemen 
FIG.  24. — Indicator  Diagrams  for  Quality  Governing. 

Otto  cycle  depends  on  the  terminal  compression  pressure 
if  the  initial  pressure  remains  constant. 

From  the  theoretical  view  point  this  method  of  govern- 
ing should,  therefore,  give  a  constant  efficiency  for  all 
loads.  Practically,  this  is  not  the  case  because  as  the 
mixture  becomes  leaner  it  burns  more  and  more  slowly,  as  is 
indicated  by  the  gradual  tipping  of  the  combustion  lines  in 
Fig.  24.  This  results  in  greater  loss  to  the  jacket  water 
at  fractional  loads,  and  ultimately,  to  the  exhaust  of 
incompletely  burned  charges  at  very  light  loads.  The 
efficiency,  therefore,  actually  decreases  as  the  load  decreases. 


70  GAS   POWER 

This  can  be  partly  counterbalanced  in  two  ways,  neither 
of  which  has  met  with  extended  practical  success.  As  the 
mixture  becomes  slower  burning,  the  time  at  which  ignition 
occurs  can  be  advanced  (made  earlier)  with  reference  to  the 
rest  of  the  cycle.  This  is  often  done  by  hand  when  an 
engine  has  to  run  for  long  periods  of  time  at  reduced  loads, 
but  has  not  yet  been  generally  adapted  to  governor  control  so 
that  the  time  of  ignition  can  be  made  to  follow  a  variable 
load.  The  other  method  is  to  draw  in  air  only  during  the 
first  part  of  the  suction  stroke  on  fractional  loads,  and  to 
follow  this  with  mixture  of  the  best  proportions  in  sufficient 
quantity  to  give  the  power  required  at  the  instant.  Dur- 
ing the  last  part  of  the  suction  stroke  and  all  of  the  com- 
pression stroke,  this  mixture  will  have  an  opportunity  to 
mix  with  the  air  drawn  in  first,  but  this  action  is  far  from 
perfect  and  a  comparatively  rich  charge  will  remain  next 
to  the  cylinder  head  and  around  the  igniters.  The  result 
is  that,  although  the  proportions  of  air  and  fuel  are  such 
as  to  give  the  lean  mixture  required  for  the  load,  most  of 
the  fuel  exists  in  a  fairly  rich  mixture  which  will  burn  rapidly. 
The  use  of  this  method  has  been  attempted  in  several 
different  ways,  but  has  always  seemed  to  lead  to  greater 
complications  than  were  warranted  by  the  results  attained. 

The  advantages  and  disadvantages  of  quality  regulation 
will  be  considered  in  connection  with  the  method  next 
described. 

44.  Quantity  Regulation.  When  carrying  full  load  an 
internal  combustion  engine  draws  into  its  cylinder  enough 
air  to  practically  completely  burn  the  fuel  charge.  It 
was  seen  that  in  quality  regulation  this  quantity  is  increased 
when  the  amount  of  fuel  is  decreased  to  obtain  fractional 
loads;  hence  with  that  method  there  is  more  than  enough 
air  present  at  all  but  the  maximum  load  and  a  slower  burn- 
ing mixture  results. 

In  quantity  regulation  this  is  obviated  by  decreasing 
the  air  supply  with  the  fuel  supply  so  that  the  mixture  has 


VII.  GOVERNING  AND  GOVERNORS 


71 


practically  the  same  proportions  or  quality  for  all  loads, 
but  varies  in  quantity  to  suit  the  demand. 

This  variation  is  generally  effected  by  throttling  the  enter- 
ing charge  of  mixture,  and  engines  operated  in  this  way 
are  often  called  throttling  engines.  There  is,  however, 
another  method  of  varying  the  quantity  which  is  known 
as  the  cut-off  method  of  governing.  The  mixture  is  drawn 
in  during  the  first  part  of  the  suction  stroke  as  though  full 
load  were  to  be  carried,  but  when  enough  has  entered  to 
supply  the  existing  demand,  the  charge  is  cut  off.  That 
already  in  the  cylinder  simply  expands  behind  the  piston 


(a)  "  Cut-off."  (6)    "  Throttling." 

FIG.  25. — Indicator  Diagrams  for  Quantity  Governing. 

during  the  remainder  of  the  suction  stroke,  and  is  then 
compressed  as  in  normal  operation. 

Of  the  two  methods,  the  straight  throttling  is  generally 
preferred,  as  it  leads  to  simple  governors  and  valve  gear. 

Diagrams  for  each  type  of  quantity  governing  are  given 
in  Fig.  25  (a),  (6).  The  former  shows  a  diagram  with  cut- 
off governing,  the  latter  with  straight  throttling. 

Theoretically,  the  efficiency  of  engines  governed  by  the 
quantity  method  should  decrease  as  the  load  falls  off, 
because  of  the  decreasing  compression  pressure  which  would 
cause  slower  burning  of  the  charge.  Practically,  the 
efficiency  falls  for  this  reason  and  also  because  of  the 


72  GAS  POWER 

increasing  negative  work  of  the  lower  loop  of  the  diagram, 
which  grows  larger  as  the  throttling  increases. 

45.  Advantages  and  Disadvantages  of  Precision  Govern- 
ing.    Both  quantity  and  quality  methods  give  regularly 
distributed  impulses  so  that  practically  the  same  weight 
of  flywheel  can  be  used  for  both,  although   there  is   the- 
oretically a  slight  advantage  in  favor  of  quantity  governing. 

Quality  governing  is  almost  ideal  for  the  higher  loads, 
but  with  low  loads  the  lean  mixtures  required  are  apt  to 
be  slow  burning  and  always  give  more  or  less  erratic  ignition 
phenomena. 

On  the  other  hand,  quantity  governing  is  best  at  light 
loads  because  the  mixture  of  most  rapid-burning  proportions 
may  be  used  and,  if  the  compression  has  not  been  too 
greatly  reduced,  there  will  be  no  difficulty  in  effecting 
ignition. 

46.  Mixed  Methods.     Many  builders  have  attempted, 
more  or  less  successfully,  to  combine  two  or  three  methods 
of  governing  so  as  to  attain  the  maximum  number  of  advan- 
tages with  the  fewest  undesirable  features.     Most  of  these 
combinations  have  been  of  questionable  merit  because  of 
the  added  complications  involved,  but  some  of  the  more 
recent  have  proved  highly  successful. 

One  practical  example  of  this  mixed  method  is  that 
used  by  the  Buckeye  Engine  Company  (see  p.  146),  which 
is  so  arranged  that  the  governing  is  practically  effected 
by  quality  changes  for  the  higher  loads,  while  for  the  lower 
loads  the  quality  is  maintained  approximately  constant  and 
the  quantity  changed.  In  this  way,  no  slow-burning 
mixtures  are  obtained,  and  the  compression  pressure  does 
not  vary  greatly  during  the  entire  range.  This  company 
has  also  devised  a  successful  method  of  shifting  the  time  of 
ignition  by  means  of  the  governor  so  that  the  charge  is 
ignited  at  the  time  best  suited  to  its  characteristics. 


CHAPTER  VIII 
IGNITION  SYSTEMS 

t 

47.  Historical.     Some    of    the    first    gas    engines    built 
were  equipped  with  electric  ignition,  but  this  rapidly  gave 
way  to  what  was   known  as  the  open-flame  ignition,  which 
was  used  in  one  form  or  another  on  all  the    early  Otto 
engines. 

This  method  depended  on  the  maintaining  of  an  open 
flame  in  an  auxiliary  chamber  so  arranged  that  it  could 
be  opened  into  the  engine  cylinder  at  the  end  of  compression, 
thus  igniting  the  charge.  The  violent  pressure  changes 
generally  extinguished  the  open  flame,  but  this  was  sub- 
sequently relighted  by  means  of  an  auxiliary  jet  which 
burned  continuously.  The  method  was  costly,  as  it  often 
consumed  as  much  as  10  per  cent  of  all  the  fuel  used  by  the 
engine  and  was  unsatisfactory  because  of  its  uncertainty, 
the  flames  frequently  being  extinguished  by  drafts  and 
other  unavoidable  occurrences. 

The  open-flame  method  was  followed  by  the  hot  tube, 
and  later,  by  the  earlier  forms  of  electric  igniters.  As  all 
of  these  are  still  in  use  in  modified  form  they  will  be  sepa- 
rately considered  in  the  following  paragraphs. 

48.  Hot-tube    Ignition.      With    this    method,    ignition 
is   caused  by  bringing  the  compressed  charge  into  contact 
with  a  heated  tube.     One  form  of  the  apparatus  is  shown 
in  Fig.  26,  and  will  serve  to  illustrate  the  description.     The 
tube  a,  which  is  made  either  of  porcelain  or  of  a  nickel 
alloy,  communicates  at  one  end  with  the  combustion  cham- 

73 


74 


GAS  POWER 


ber  as  shown.     It  is  heated  near  its  closed  end  by  means 
of  the  Bunsen  burner  b. 

After  an  exhaust  stroke  has  been  completed,  the  clearance 
space,  of  which  the  tube  forms  a  part,  is  always  filled  with 
burned  gases.  During  the  suction  stroke  of  the  piston,  the 
gases  in  the  tube  remain  practically  stagnant  and  do  not 
mix  to  any  appreciable  extent  with  the  fresh  charge  being 


FIG.  26.— Hot  Tube  I  gn  it  ion. 


admitted.  During  the  following  compression  stroke,  some 
of  the  fresh  charge  is  compressed  into  the  tube,  partly  com- 
pressing the  burned  gases  ahead  of  it  and  partly  mixing 
with  them.  Ultimately,  an  ignitable  mixture  will  arrive 
at  a  point  in  the  tube  which  is  at  a  high  enough  tem- 
perature to  fire  it.  When  this  occurs,  the  flame  strikes 
back  along  the  tube  and  ignites  the  compressed  charge  in 
the  clearance. 

By  properly  regulating  the  location  of  the  hot  zone  on 


VIII.     IGNITION  SYSTEMS  75 

the  tube  and  its  temperature,  the  ignition  can  be  made  to 
occur  at  any  desired  point  near  the  end  of  the  compression 
stroke.  Such  timing  is  effected  by  sliding  the  burner  and 
chimney  in  or  out  on  the  post  c,  to  set  the  location  of  the 
hot  zone,  and  by  regulating  the  burner  to  fix  the  tem- 
perature. The  hot  zone  is  nearly  always  maintained  at 
about  a  dull  red. 

Hot-tube  ignition  possesses  the  advantages  of  being 
very  simple  and  very  certain,  but  it  is  open  to  the  two  fol- 
lowing serious  objections:  It  entails  the  use  of  5  per  cent 
or  more  of  all  the  heat  supplied  a  small  engine,  and  timing 
can  never  be  very  exact  because  of  varying  degrees  of  churn- 
ing of  the  gases,  varying  temperatures,  and  varying  propor- 
tions or  quality  of  mixture.  Several  attempts  have  been 
made  to  obtain  exact  timing  by  the  use  of  some  sort  of 
valve  which  would  close  the  tube  off  from  the  combustion 
space  until  ignition  was  desired,  but  these  constructions  have 
generally  been  abandoned  because  of  the  mechanical  dif- 
ficulties encountered. 

Hot-tube  ignition  is  now  seldom  used,  as  such,  in  this 
country,  having  been  superseded  by  the  more  exact,  and 
almost  equally  reliable,  electrical  methods.  It  is,  how- 
ever, occasionally  found  on  engines  used  where  fuel  is 
plentiful,  as  in  the  natural-gas  fields,  because  of  its  low 
first  and  maintenance  costs  and  because  of  its  great  sim- 
plicity. £ 

A  modified  type  of  not-tube  ignition  which  in  its  various 
forms  may  be  called  hot-head,  hot-bulb,  or  hot-disk  igni- 
tion, is  used  to  a  considerable  extent  with  oil  engines  and 
will  be  described  in  connection  with  such  apparatus  in 
Chapter  XIII. 

49.  Electric  Ignition.  There  are  a  great  number  of 
kinds  or  systems  of  electric  ignition  but  the  scope  of  this 
book  does  not  permit  of  more  than  a  very  cursory  examina- 
tion of  the  field.  For  this  purpose  we  shall  first  divide  the 
numerous  systems  into  two  classes  which  may  be  called 


76  GAS  POWER 

low-tension  and  high-tension  methods.  Typical  simple 
examples  of  each  class  are  given  in  the  following  para- 
graphs. 

(a)  LOW-TENSION  IGNITION. 

In  all  low-tension  ignition  systems,  a  low-voltage  source 
of  electrical  energy  is  used.  This  source  may  be  anything 
from  the  simplest  of  dry  batteries  to  the  most  complicated 
small  electric  generator  or  dynamo  or  the  most  expensive 
form  of  low-voltage  magneto.  The  tension  which  must  be 
available  in  the  average  case  is  about  five  to  six  volts,  and 
the  resistance  of  the  circuit  is  such  that  from  one  to  two 


Movable  grounded, 
electrode 


I 

FIG.  27. — Low-tension  Ignition  System. 

amperes,  or  in  extreme  cases  as  high  as  five  amperes,  flow 
when  the  circuit  is  closed. 

In  Fig.  27  are  shown  the  essential  parts  of  a  low-tension 
system  of  the  simplest  type.  With  the  switch  closed, 
current  will  flow  through  the  circuit  whenever  the  "  elec- 
trodes "  which  are  enclosed  in  the  combustion  space  of  the 
engine  are  brought  into  contact.  When  such  a  condition 
exists,  the  sudden  breaking  of  contact  between  the  electrodes 
will  cause  a  spark  to  pass  between  them,  and  if  this  occurs 
near  the  end  of  the  compression  stroke  when  the  electrodes 
are  surrounded  by  highly  compressed  combustible  mixture, 
ignition  will  be  effected. 


VIII.     IGNITION  SYSTEMS  77 

The  passing  of  the  spark  is  due  to  the  action  of  the  coil 
which  is  variously  known  as  a  "  reactance,"  an  "  intensify- 
ing/' or  a  "  kick  "  coil.  This  consists  essentially  of  a  num- 
ber of  turns  of  insulated  wire  around  a  soft  iron  core.  On 
account  of  the  inductive  action  of  such  a  coil  a  momentary 
increase  of  voltage  is  caused  when  the  circuit  is  broken  by 
the  motion  of  the  moving  electrode. 

Systems  of  this  type  are  often  designated  as  "  make- 
and-break  "  ignition  systems,  because  of  the  action  of  the 
electrodes. 

It  will  be  observed  that  the  apparatus  of  the  make-and 
break  system  is  electrically  very  simple.  Mechanically  it 
is  more  or  less  complicated,  in  the  real  case,  by  the  appara- 
tus necessary  to  give  proper  motion  to  the  electrode  and  by 
the  devices  which  must  be  used  in  order  to  prevent  leakage 
of  the  compressed  mixture  around  the  movable  electrode 
where  it  enters  the  cylinder.  For  high  engine  speed, 
extremely  refined  design  is  required  in  order  that  inertia 
effects  may  not  prevent  the  satisfactory  operation  of  the 
moving  electrode. 

In  Fig.  28  is  shown  a  typical  igniter  of  the  make-and- 
break  type,  together  with  the  method  of  operating  it.  The 
contact  is  made  between  the  points  on  the  electrodes  when 
the  flipper  F  moving  to  the  left  (in  the  figure)  engages  the 
hammer  trigger,  overtravel  being  permitted  by  the  spring 
Sj  which  fastens  the  hammer  trigger  to  the  movable  elec- 
trode. When  the  flipper  F  has  traveled  so  far  to  the  left 
that  it  disengages  the  hammer  trigger,  the  spring  S'  rotates 
the  movable  electrode,  thus  suddenly  breaking  the  circuit 
at  the  contact  points  within  the  cylinder. 

Timing  is  effected  by  sliding  the  block  B  along  the  rod 
R  and  fastening  it  at  an  appropriate  position  by  means  of 
the  screw  shown. 

Igniters  in  which  the  electrodes  make  and  break  contact 
in  the  way  shown  in  these  figures  are  often  called  hammer 
"  make-and-break "  igniters  to  distinguish  them  from 


78 


GAS  POWER 


a  variety  described  in  the  next  paragraph.  There  is,  how- 
ever, some  uncertainty  in  the  use  of  this  term,  as  it  is  used 
by  many  to  designate  a  type  similar  to  that  just  described, 
but  operating  in  such  a  way  that  the  electrodes  are  separated 
by  the  hammer  action  of  a  spring-actuated  piece  striking  a 
trigger  on  the  movable  electrode. 


Spring—^-; 

s 


Movable 
Electrode 


Spring  S' 


Hammer. 
Trigger 


MS  ill. -i ted 
Electrode 


.lating  Washer* 


Engine 
Cylinder 


Valve  and 
Igniter  Shaft 


(6)  Method  of  Operation  on  Engine 


Movable 
Electrode 


Steel 
Stop  Pin 


Insulated 
Electrode 


Contact.  Points 


FIG.  28. — Hammer  Type — "  Make-and-Break  "  Igniter. 

There  is  another  type  of  make-and-break  igniter  plug 
known  as  a  wipe-spark  plug,  one  example  of  which  is  shown 
in  Fig.  29.  This  is  the  type  used  by  the  Foos  Gas  Engine 
Company,  and  is  favored  by  this  company  on  the  ground 
that  the  rubbing  of  one  electrode  over  the  other  keeps 
both  clean  and  free  from  carbon,  oil  and  other  deposits, 
which  with  the  type  already  described  may  cause  imperfect 
action. 

There  are  also  a  number  of  magnetically  (or  electrically) 
operated  make-and-break  plugs  designed  to-  make  the 


VIII.     IGNITION  SYSTEMS 


79 


plug  a  self-contained  mechanism,  which  need  only  be 
wired  to  the  source  of  the  current  and  a  timing  device, 
thus  eliminating  push  rods,  cams,  and  other  light,  but 
numerous  mechanical  parts.  This  type  of  igniter  is 
generally  constructed  in  such  a  way  that  the  electric 
circuit  energizes  an  electro-magnet  which  causes  the  motion 


FIG.  29.— The  Foos  Patent  Wiping  Contact  Igniter. 

of  the  electrode  and  also  serves  as  a  kick  or  reactance  coil. 
One  example  of  such  a  plug  as  made  by  the  Bosch  Magneto 
Company,  for  operation  in  connection  with  certain  of  their 
magnetos,  is  shown  in  Fig.  30. 

The  thread  on  the  nut  A  screws  into  the  engine  cylinder, 
bringing  the  movable  electrode  E  and  the  stationary 
electrode  E'  within  the  clearance  space.  The  two  electrodes 
are  forced  into  contact  by  the  spring  S,  which  presses  on  the 


80 


GAS  POWER 


movable  electrode  just  below  the  knife-edge  pivot  in  the 
piece  K.  The  movable  electrode  E  is  drawn  out  of  contact 
by  magnetic  action,  which  draws  its  upper  end  toward  the 
right.  This  occurs  at  the  instant  at  which  a  spark  is  de- 
sired, and  because  of  the  current  flowing  in  the  coil  C  en- 
closed within  the  head  B  of  the  plug. 


FIG.  30.— Bosch  Magneto— "  Make  and  Break"  Plug. 


HIGH-TENSION  IGNITION. 

It  will  have  been  observed  that  the  apparatus  used  with 
low-tension  ignition  is  designed  to  first  close  and  then  open 
an  electric  circuit,  the  spark  passing  when  the  circuit  is 
broken  and  at  the  point  (within  the  cylinder)  at  which 
it  is  broken.  In  the  high-tension  system,  on  the  other  hand, 
the  apparatus  is  arranged  to  build  up  so  high  an  electrical 
potential  that  a  spark  may  be  made  to  jump  across  a 
permanent  gap  in  the  electric  circuit.  This  gap  is  located 
within  the  combustion  space  of  the  engine  and  the  spark 
therefore  serves  to  ignite  the  compressed  charge. 


VIII.    IGNITION  SYSTEMS  81 

The  simplest  possible  arrangement  of  such  a  system  is 
shown  in  Fig.  31.  There  are  two  distinct  electric  circuits, 
a  low-tension  circuit,  shown  by  heavy  lines,  and  a  high-ten- 
sion circuit,  shown  by  light  lines. 

The  essential  parts  of  this  system  as  shown  in  the  figure 
are  a  contactor  or  timer  T,  a  source  of  current  such  as  a 
battery  B,  a  transformer  coil  C,  and  a  spark  plug,  S.  The 
coil  is  wound  with  a  number  of  turns  of  comparatively 
heavy  wire  which  form  part  of  the  primary  circuit  and  with 
a  greater  number  of  turns  of  finer  wire  which  form  part  of 
the  secondary  circuit.  It  is  essentially  a  transformer, 


Secondary  Circuit 


FIG.  31. — High-tension  Ignition  Circuit. 

producing  high  voltages  in  the  secondary  winding  when  low 
voltages  are  impressed  on  the  primary. 

In  operation,  the  contactor  or  timer  T  closes  the  primary 
circuit  when  it  rotates  into  the  position  shown  and  then 
suddenly  breaks  this  circuit  when  the  cam  rotates  out 
from  under  the  spring-pressed  trigger.  This  sudden  break- 
ing of  the  circuit  induces  a  voltage  in  the  secondary  which 
is  sufficiently  high  to  cause  a  spark  to  jump  across  the  gap 
in  the  spark  plug  within  the  cylinder,  thus  causing  ignition. 
It  should  be  noted  that  the  timer  shown  is  merely  a  diagram- 
matic representation  of  the  real  mechanism  and  is  not 
intended  to  represent  an  operative  device. 

This  system,  while  correct  as  far  as  it  goes,  is  hardly 


82 


GAS  POWER 


commercial  and  must  be  considerably  modified  in  practice. 
There  are  so  many  modifications  now  in  use  that  it  is  not 
possible  in  a  book  of  this  scope  to  give  even  a  brief  account 
of  the  more  common;  it  seems  advisable,  therefore,  to 
describe  one  in  some  detail,  so  as  to  indicate  the  various 
practical  modifications  and  the  types  of  connections. 

The  principal  modification  is  the  addition  of  a  so-called 
"  trembler  "  to  interrupt  the  primary  circuit  for  the  purpose 
of  obtaining  quicker  operation  and  hence  a  more  perfect 
spark.  This  trembler  is  merely  a  spring  contact,  which 
is  normally  in  position  to  close  the  primary  circuit,  but  is 


Condenser 


Eng-iue 
Metal 


;FIG    32. — High-tension  Ignition  System  with  Trembler  Coil. 

drawn  out  of  that  position  by  the  magnetic  action  of  the 
core  of  the  transformer  coil  as  soon  as  the  latter  becomes 
magnetized  by  the  primary  current.  A  system  containing 
such  a  device  is  shown  in  Fig.  32.  In  operation  the  primary 
current  flows  through  the  stationary  block  TF,  the  screw 
U,  the  trembler  X,  the  primary  winding  on  the  coil, 
and  back  to  the  battery  whenever  the  timer  T  makes  con- 
tact by  rotating  into  the  position  shown.  The  flow  of  cur- 
rent, however,  magnetizes  the  soft  iron  core  of  the  coil  C, 
and  this  pulls  the  spring  X  toward  the  coil,  breaking  the 
primary  circuit  and  causing  a  spark  to  jump  the  gap  in  the 
secondary  circuit  as  before.  By  proper  design,  the  trembler 


VIII.     IGNITION  SYSTEMS  83 

can  be  made  to  operate  very  rapidly,  thus  giving  a  very 
rapid  break  and  a  very  perfect  and  well-timed  spark  even 
at  high  engine  speeds.  The  work  of  the  timer  is  propor- 
tionately simplified,  as  it  now  performs  only  the  function 
of  closing  the  circuit  in  order  that  the  spark  may  be  caused 
to  pass  at  the  desired  time  and  of  opening  the  circuit  later 
when  further  sparks  would  be  useless.  It  should  be  noted 
that  a  series  of  sparks  may  be  made  to  jump  the  gap  in  the 
cylinder  if  the  trembler  X  operates  rapidly  and  the  timer  T 
maintains  contact  for  an  appreciable  length  of  time. 

The  condenser  shown  as  connected  across  the  blocks 
V  and  W  consists  of  alternate  sheets  of  metal  foil  and  insulat- 
ing material.  The  diagrammatic  representation  shows 
only  the  sheets  of  metal  foil,  and  it  will  be  observed  that 
alternate  sheets  are  connected  together.  The  condenser 
serves  to  absorb  electrical  surges  in  the  primary  circuit 
which  result  from  the  rapid  breaking  at  the  trembler.  If 
it  were  not  present,  the  contact  points  on  the  trembler 
X  and  the  screw  V  would  rapidly  deteriorate  or  even  pos- 
sibly fuse  together  because  of  the  formation  of  an  arc  during 
the  break. 

The  essential  parts  of  a  high-tension  spark  plug  are 
shown  in  Fig.  33.  The  central  post,  terminal,  or  electrode 
is  insulated,  as  shown,  from  the  metal  part  of  the  plug. 
This  metal  carries  the  other  electrode  and  makes  contact 
with  the  metal  of  the  engine,  which  thus  serves  as  part  of 
the  high-tension  circuit. 

There  are  a  great  number  of  high-tension  systems  in 
which  the  parts  shown  in  Fig.  31  do  not  seem  to  be  present, 
the  system  apparently  comprising  a  magneto  which  serves 
as  a  generator  of  current,  the  spark  plugs  and  the  connecting 
cables.  In  such  cases,  the  transformer  coil  is  incorporated 
in  the  armature  of  the  magneto,  and  the  various  condensers 
and  current-making  and  breaking  devices  are  similarly  built 
into  its  structure.  Such  magnetos  must  be  positively 
driven  from  the  engine  by  a  gear  or  chain,  and  the  same  state- 


84 


GAS  POWER 


ment  is  true  with  regard  to  the  timer  when  a  separate  device 
is  used  for  this  purpose.  In  this  way  only,  can  the  sparks 
be  made  to  pass  at  the  proper  time  in  the  cylinder  or  cylin- 
ders of  the  engine. 


Insulated  Foot 
or  Terminal. 

Insulating  Material 


Grounded  Terminal. 
Spark  Gap 


FIG.  33. — High-tension  Spark  Plugs. 

Adjustment  of  the  timing,  that  is,  advancing  or  retard- 
ing the  spark  with  respect  to  the  crank  and  piston  positions, 
is  effected  by  swinging  some  part  of  the  timing  device  about 
the  part  which  is  thus  positively  driven.  If  the  part  is 
swung  ahead  in  the  direction  of  the  rotation  of  the  latter, 
the  spark  is  retarded,  and  vice  versa. 


CHAPTER  IX 
CARBURETING  AND  CARBURETERS 

50.  The  Liquid-fuel  Problem.     When  an  internal  com- 
bustion engine  is  supplied  with  gaseous  fuel  such  as  natural 
gas  or  producer  gas,  the  problem  of  mixing  that  gas  with 
the  necessary  air  and  of  introducing  the  mixture  into  the 
cylinders  is  comparatively  simple.     The  problem  presented 
when  the  fuel  is  initially  in  liquid  form  is,  however,  more 
complicated.     Liquid  fuel  will  not  burn  in  the  liquid  form; 
it  must  first  be  vaporized.     The  problem  which  must  be 
solved  in  handling  liquid  fuels  is  therefore  twofold:    (a) 
the  liquid  must  be  vaporized,  and  (6)  this  vapor  must  be 
mixed  with  the  necessary  air  to  form  the  combustible  mixture. 

With  very  volatile  fuels,  such  as  gasoline,  little  dif- 
ficulty is  experienced  in  thus  forming  a  combustible  mixture, 
but  kerosene  and  heavier  liquid  fuels  are  not  as  easily 
handled,  in  fact  there  are  comparatively  few  methods  of 
operation  which  give  satisfactory  results  with  fuels  heavier 
than  kerosene.  The  methods  used  with  the  more  volatile 
liquids  will  be  considered  in  this  chapter  and  several  engines 
capable  of  handling  the  heavier  fuels  will  be  described  later. 

51.  Types    of    Gasoline    Carbureters.     The    principal 
highly  volatile  fuel  used  in  this  country  is  gasoline,  and  the 
apparatus  adapted  to  its  use  will  first  be  considered.     With 
this  material,  a  perfectly  satisfactory  mixture  of  air  and 
vapor  can  be  made  very  quickly  and  at  ordinary  temper- 
atures by  simply  injecting  the  liquid  into  the  air  on  its  way 
to  the  engine.     Devices  arranged  to  thus  inject  fuel  into 
the  air  may  be  classified  under  the  broad  head  of  jet  car- 

85 


86  GAS  POWEK 

bureters.  They  are  almost  the  only  kind  at  present  in 
use  in  this  country,  although  very  satisfactory  carbureting 
devices  of  other  kinds  have  been  made  and  used.  Thus  a 
vessel  in  which  the  air  on  its  way  to  the  engine  is  made  to 
bubble  through  the  liquid  may  be  made  to  give  satisfac- 
tory results.  It  is  called  a  bubbling  carbureter.  Or  a 
vessel  in  which  the  air  is  drawn  over  wicks  wet  with  gasoline 
might  be,  and  has  been,  used.  Such  devices  are  called 
wick  carbureters.  There  is  also  a  kind  of  mixing  device 
known  as  a  puddle  carbureter.  As  several  of  this  type  are 
in  use  in  this  country  an  example  will  be  given  after  con- 
sidering jet  carbureters. 

52.  Jet  carbureters,  (a)  Several  of  the  simplest  forms 
of  jet-mixing  or  carbureting  devices  for  use  on  stationary 
engines  are  shown  in  Fig.  34  (a),  (6)  and  (c).  The  gasoline 
is  pumped  into  the  reservoir  from  a  storage  tank  at  a  more 
rapid  rate  than  it  is  used,  so  that  it  continuously  overflows 
and  thus  maintains  a  constant  level  in  the  reservoir.  The 
overflow  is  set  so  that  this  level  is  just  below  the  tip  of  the 
gasoline  nozzle.  This  nozzle  enters  the  air  pipe  leading 
to  the  inlet  valve  of  the  engine  as  in  (6),  or  is  centered  in 
that  pipe  as  in  (a)  and  (c).  The  diameter  of  the  pipe  is 
often  reduced  at  this  point  as  shown  in  (c).  During  the 
suction  stroke  of  the  engine,  the  pressure  within  the  air 
pipe  is  reduced  below  that  of  the  atmosphere,  and  the  air 
rushing  past  the  nozzle  creates  an  additional  slight  pressure 
drop  immediately  opposite  the  end  of  the  latter.  As  a 
result  of  this  double  reduction  of  pressure  opposite  the  end 
of  the  nozzle,  a  small  jet  of  gasoline  is  discharged  into  the 
air  current  by  atmospheric  pressure  on  the  liquid  surface 
in  the  reservoir.  The  quantity  thus  discharged  can  be 
regulated  for  any  velocity  of  air  by  means  of  the  needle 
valve  shown.  When  hit-and-miss  governing  is  used,  it  is 
obvious  that  no  fuel  need  be  drawn  out  of  the  nozzle  and 
hence  wasted  during  missed  cycles.  When  throttling 
governing  is  used,  the  throttle  valve  may  be  placed  on  the 


IX.  CARBURETING  AND  CARBURETERS 


87 


engine  side  of  the  carbureter,  thus  controlling  the  quantity 
and  velocity  of  air  flowing  through  the  latter  and  indirectly 
controlling  the  amount  of  gasoline  discharged  into  that  air. 
The  construction  of  the  air  pipe  as  shown  in  (c)  is  called 
a  throat  or  Venturi  tube  and  is  used  to  increase  the  velocity 
immediately  around  and  above  the  nozzle,  thus  decreasing 
the  pressure  and  making  a  greater  head  available  for  caus- 
ing flow. 

Mixture  to 
Cylinder 

tt 


Gasoline  Tank 


Venturi  Tribe 


FIG.  34. — Simple  Forms  of  Jet  Carbureters. 


Another  simple  form  of  jet  carbureter  known  as  a  car- 
bureting valve  is  shown  in  Fig.  35.  The  light  disk  or  poppet 
valve  with  its  seat  is  inserted  in  the  air  pipe  and  closes  off 
the  air  and  gasoline  supply  as  shown.  During  the  suction 
stroke,  this  valve  is  raised  by  atmospheric  pressure,  thus 
uncovering  the  gasoline  inlet,  and  a  jet  of  the  liquid  then 
shoots  into  the  column  of  air  passing  through  the  valve. 
The  gasoline  may  be  supplied  from  a  constant-head  reservoir 


88 


GAS  POWER 


with  the  level  slightly  below  the  discharge  point,  or  preferably 
under  slight  pressure,  as  under  natural  head,  or  by  air  pressure 
on  the  surface  of  liquid  in  a  closed  reservoir. 

Carbureting  valves  do  not,  in  general,  form  as  perfect 
a  mixture  as  do  the  other  types  with  central  nozzles,  so 
that  they  are  most  often  used  with  the  smaller,  two-stroke 
engines  with  crank-case  compression.  In  such  cases, 


FIG.  35. — Carbureting  Valve. 


the  churning  of  the  mixture  in  the  crank  case  and  in  the 
by-pass  tend  to  perfect  the  mixture. 

There  are  many  possible  modifications  of  the  two  types 
already  described,  and  because  of  their  simplicity  and  ease 
of  adjustment  they  are  very  widely  used  in  stationary  prac- 
tice. Carbureting  valves  are  also  used  on  the  smaller 
and  cheaper  two-stroke  marine  engines. 

It  will  be  observed  that,  if  uniform  results  are  to  be 
obtained,  the  head  of  gasoline  at  the  nozzle  must  be  main- 
tained practically  constant.  This  is  achieved  with  com- 


IX.  CARBURETING  AND  CARBURETERS 


parative  ease  in  stationary  practice  by  the  means  already 
suggested,  but  carbureters  for  use  on  automobiles  and 
the  better  types  of  marine  engines  require  further  refine- 
ment because  of  the  constant  tipping  and  vibration  to 


Mixture  In. 


Float 


Air  In. 


la  Valve 
Gasoline  In. 

FIG.  36a — "  Float-feed  "  Jet  Carbureter.    Off-set  Float. 


Mixture  to 
Engine 

Throttle  Disk 


Gasoline  In. 

FIG.  366. — "Float-feed  "  Carbureter.    Concentric  Float. 

which  the  carbureter  and  engine  are  subjected.  In  such 
cases,  some  sort  of  "  float-feed  "  carbureter  is  therefore 
commonly  used.  Examples  of  such  carbureters  are  shown 
in  Fig.  36  (a)  and  (b).  The  function  of  the  float  is  to 
regulate  the  level  of  gasoline  in  the  bowl  of  the  carbureter, 


90  GAS  POWER 

by  opening  and   closing  the  small   control  valve  shown 
The  form  in  which  the  float  is  annular  and  surrounds  the 
nozzle  is  the  better  of  the  two,  as  it  comes  nearest  to  main- 
taining a  constant  level  on  the  nozzle  at  its  center  when  the 
engine  and  carbureter  are  tipped  at  a  considerable  angle. 

Engines  of  the  automobile  and  marine  types  are  gener- 
ally required  to  operate*  satisfactorily  over  a  very  wide 
range  of  speeds  and  loads,  and  experience  shows  that  the 
simple  float-feed  carbureters  shown  in  Fig.  36  must,  in 
general,  be  still  further  modified  to  meet  such  conditions. 
The  reason  for  this  is  the  fact  that,  as  the  speeds  and  loads 
change,  the  same  setting  of  the  needle  valve  will  not  give 
the  same  quality  of  mixture  because  of  the  wide  variation 
in  the  suction  effect  on  the  nozzle  accompanying  wide 
variation  of  the  quantity,  and  hence  the  velocity,  of  air 
flowing  by  that  nozzle.  As  it  is  not  convenient  or  practicable 
to  constantly  regulate  the  needle  valve,  many  attempts 
have  been  made  to  build  a  carbureter  which  will  automatically 
maintain  the  proper  mixture.  Most  of  these  devices  are 
based  on  the  construction  of  a  carbureter  which  would  nor- 
mally give  too  rich  a  mixture  when  operating  at  high  speed, 
and  then  adding  to  this  a  device  which  will  admit  to  the 
suction  pipe  above  the  carbureter  more  and  more  uncar- 
bureted  air  as  the  speed  increases.  As  this  auxiliary  air 
supplies  part  of  the  air  entering  the  engine,  less  flows  by 
the  nozzle,  so  that  the  richness  of  the  mixture  decreases 
in  two  ways:  the  suction  on  the  nozzle  decreases  as  less  air 
is  required  to  flow  around  it,  and  the  mixture  formed  is 
later  diluted  by  admixture  of  the  auxiliary  or  secondary 
air.  Other  devices  employ  two  gasoline  nozzles  and 
arrange  to  have  one  or  both  operative,  as  instantaneous 
conditions  require. 

In  general,  it  can  be  said  that  no  one  form  will  operate 
successfully  on  all  engines.  Each  carbureter  has  its  in- 
dividual characteristics,  and  the  same  is  true  of  each  engine 
and  each  engine  operator.  When  all  three  sets  of  char- 


IX.  CARBURETING  AND  CARBURETERS 


91 


acteristics  approximately  agree,  successful  operation  is 
assured;  when  they  do  not,  another  combination  may  give 
better  results. 

53.  Puddle  Carbureters.  A  form  of  puddle  carbureter  is 
shown  in  Fig.  37.  The  air  rushing  through  the  distorted 
Venturi  on  the  way  to  the  engine  impinges  on  the  surface 
of  the  puddle  of  gasoline  at  the  bottom  of  the  bend  and 
picks  up  some,  or  all,  of  it,  depending  upon  the  velocity 
with  which  it  happens  to  be  moving.  Such  puddle  devices 
have,  in  some  instances,  been  combined  with  jets  operating 
like  those  already  described,  the  dimensions  and  levels 


Air  In. 


Mixture 


Engine 


Float 


FIG.  37.—"  Puddle  "  Carbureter. 


being  so  chosen  as  to  obtain  desirable  characteristics  for 
variable-speed  work. 

54.  Carbureting  Kerosene.  It  is  now  necessary  to 
study  in  more  detail  the  phenomena  occurring  during  car- 
bureting. In  the  jet  form  of  carbureter  the  fuel  in  liquid 
form  is  injected  into  the  air.  It  is  then  mechanically 
carried  by  this  air,  just  as  dust  is  carried  in  the  atmosphere, 
until  it  has  had  time  to  vaporize.  When  this  has  occurred, 
the  fuel  has  become  gaseous  and  is  carried  along  in  the  air 
just  as  though  it  were  a  part  of  that  air. 

But  vaporization  of  gasoline,  like  vaporization  of  water 
or  of  any  other  liquid,  requires  the  addition  of  heat;  i.e., 
the  so-called  latent  heat  of  vaporization.  In  the  case  of  gaso- 


92  GAS  POWER 

line,  the  quantity  of  heat  required  is  small  and  can,  under 
ordinary  conditions,  be  taken  from  the  air  being  carbureted 
without  reducing  the  temperature  of  the  latter  to  an  abnor- 
mal value.  If,  however,  the  air  is  initially  at  a  very  low 
temperature,  as  in  cold  winter  weather,  its  temperature 
just  beyond  the  nozzle  in  the  carbureter  may  be  reduced 
to  a  very  low  value  and  trouble  may  occur  in  two  ways: 
the  air  may  not  be  able  to  give  up  enough  heat  to  vaporize 
all  the  gasoline  it  has  drawn  out  of  the  nozzle  and  trouble 
may  ensue  from  its  collection  as  liquid  in  the  piping;  and 
the  temperature  may  get  so  low  as  to  precipitate  water  from 
the  air  in  the  form  of  ice. 

Difficulties  of  this  kind  are  generally  overcome  by 
preheating  the  air  and  by  heating  the  carbureter.  The  former 
is  generally  achieved  by  drawing  the  air  around  the  hot 
cylinders  or  exhaust  pipe  on  its  way  to  the  carbureter; 
the  latter,  by  jacketing  the  carbureter  with  water  from  the 
engine  jacket.  In  any  case,  arrangements  should  be  so 
made  that  the  heating  devices  can  be  made  inoperative 
in  warm  or  normal  weather,  as  the  power  of  the  engine  will 
be  decreased  if  very  hot  air  is  supplied  to  it.  This  can  easily 
be  seen  to  be  the  case  when  it  is  remembered  that  the  power 
of  the  engine  will  depend  directly  on  the  quantity  of  gasoline 
which  can  be  burned  in  its  cylinders,  and  this  will  depend 
upon  the  weight  of  air  present,  but  the  weight  of  air  present 
in  a  cylinder  of  a  given  size  will  decrease  as  the  temperature 
of  that  air  increases. 

Kerosene  cannot,  in  general,  be  satisfactorily  used 
with  such  simple  apparatus  as  that  just  described.  It  is 
true  that  almost  any  gasoline  engine  which  has  been 
operated  long  enough  to  have  attained  an  average  oper- 
ating temperature  can  be  made  to  continue  in  operation 
on  a  kerosene  and  air  mixture  formed  in  a  gasoline  car- 
bureter. The  operation  will,  however,  be  more  or  less 
uncertain  and  it  will,  in  general,  be  only  a  matter  of  a  few 
days  before  the  interior  of  the  cylinder  is  covered  with  a 


IX.  CARBURETING  AND  CARBURETERS     93 

thick  deposit  of  carbon  and  the  piston  rings  are  gummed 
or  even  burned  tight  in  their  grooves.  Preheating  of  the 
air  and  jacketing  of  the  carbureter  will  generally  minimize 
the  difficulty,  but  will  not  entirely  overcome  it. 

Kerosene  is  less  volatile  than  gasoline  at  ordinary  tem- 
peratures and  pressures,  that  is,  it  does  not  vaporize  as 
readily  and  requires  a  larger  supply  of  heat  when  it  does 
vaporize.  When  used  in  an  ordinary  carbureter,  the  liquid 
jet  is  carried  satisfactorily  by  the  air  just  as  is  the  gasoline 
jet,  but  it  is  not  as  readily  vaporized  and,  in  general,  a 
large  amount  of  it  will  enter  the  cylinder  as  a  liquid.  Some 
may  even  deposit  in  the  air  pipe  on  the  way  to  the  engine. 

Part  of  the  material  entering  the  cylinder  as  liquid  will 
generally  remain  such  until  combustion  has  started.  When 
this  occurs,  the  high  temperature  will  of  course  tend  to 
vaporize  this  liquid,  but  there  is  also  another  process  known 
as  "  cracking  "  which  goes  on  simultaneously.  "  Cracking  " 
consists  of  the  breaking  up  of  the  molecules  of  the  liquid 
kerosene,  some  of  the  resultant  products  being  finely 
divided  carbon  and  heavy,  viscous,  or  tarry  liquids.  It  is 
the  carbon  and  these  heavy  liquids  that  cause  the  difficulty 
previously  referred  to  by  gradually  collecting  within  the 
cylinder.  Obviously  anything  which  will  assist  vaporiza- 
tion will  better  the  conditions,  hence  the  benefit  derived  from 
preheating. 

The  more  the  kerosene  is  broken  up,  that  is,  the  more 
perfectly  it  is  "  atomized  "  or  sprayed  into  the  air,  the  less 
chance  will  there  be  for  collection  of  the  liquid  on  solid 
surfaces  and  the  more  rapid  will  be  the  vaporization  within 
the  cylinder  of  the  engine.  Fine  spraying  is  therefore 
advantageous,  and  any  jet  carbureter  will  work  best  when 
the  pressure  available  for  causing  flow  is  so  great  that  the 
needle  valve  must  be  almost  entirely  closed. 

It  has  also  been  found  by  experience  that  if  a  large 
amount  of  water  vapor  or  a  finely  divided  water  spray  is 
mixed  with  the  kerosene-air  mixture,  conditions  are  materially 


94  GAS  POWER 

improved.  No  really  satisfactory  explanation  of  the  full 
action  of  the  water  vapor  has  yet  been  offered,  but  it  seems 
probable  that  it  is  very  complicated  and  of  a  physical  as 
well  as  a  chemical  nature. 

The  use  of  water  makes  possible  the  use  of  high  com- 
pression without  danger  of  preignition  and  thus  makes 
possible  the  attainment  of  high  efficiency.  This  is  probably 
due  to  the  fact  that  the  water  absorbs  heat  during  com- 
pression, thus  keeping  the  temperature  below  that  which 
would  cause  spontaneous  ignition,  and  there  may  also  be 
some  sort  of  chemical  action  whereby  the  presence  of  the 
water  prevents  the  breaking  up  of,  or  the  combination  of, 
certain  of  the  constituents  of  the  fuel  to  form  compounds 
with  very  low  ignition  temperatures.  The  presence  of  water 
vapor  also  makes  the  combustion  less  "  snappy,"  that  is 
it  retards  it,  or  makes  it  slower,  so  that  the  maximum 
pressure  attained  is  lower  and  the  operation  of  the  engine 
is  made  "  smoother."  This  is  also  probably  due  to  the 
physical  absorption  of  heat  by  the  water  vapor,  which  has 
a  comparatively  high  specific  heat,  but  it  may  be  due  to  a 
certain  amount  of  dissociation  of  the  water  as  well. 

The  presence  of  water  vapor  also  tends  to  prevent 
the  deposit  of  carbon  in  the  cylinder  and  to  make  combus- 
tion more  perfect,  so  that  the  exhaust  is  clear  instead  of 
smoky. 

Even  with  the  addition  of  water  vapor,  however,  the 
operation  of  most  carbureting  kerosene  engines  cannot 
be  said  to  be  absolutely  satisfactory,  as  considerable  hand 
control  of  the  mixture  is  required  if  excessive  carbon  deposit 
and  smoky  exhaust  are  to  be  avoided  when  operating  under 
widely  varying  loads.  Most  of  these  engines  are,  however, 
perfect  enough  to  be  considered  good  commercial  prop- 
ositions. 

Some  engines  of  this  general  type  are  marketed  for  use 
with  petroleum  fuels  still  lower  in  the  scale  than  kerosene, 
many  makers  guaranteeing  satisfactory  operation  on  dis- 


IX.  CARBURETING  AND  CARBURETERS     95 

tillates  of  39°  Be*,  or  lower.  In  general,  the  difficulties 
met  increase  as  the  specific  gravity  of  the  fuel  increases, 
that  is  as  its  gravity  expressed  on  the  Be.  scale  decreases, 
and  most  engines  of  the  carbureting  type  give  smoky 
exhausts  and  carbon  deposits  if  operated  on  fuels  heavier 
than  highly  refined  kerosenes. 

Examples  of  carbureting  kerosene  engines  and  of  other 
types  adapted  to  the  use  of  heavier  fuels  will  be  described 
in  Chapter  XIII. 


CHAPTER  X. 
GAS  PRODUCERS. 

55.  The  Manufacture  of  Producer  Gas.  (a)  Simple 
Theory.  In  a  previous  chapter  on  fuels,  a  brief  description 
of  "  producer  gas  "  was  given,  without  reference  to  the 
theory  or  to  the  practical  methods  of  manufacture.  The 
fundamentals  underlying  the  production  of  this  gas  are  very 
simple,  although  the  actual  chemical  reactions  taking  place 
within  the  producer  are  complex. 

"  Producer  gas,"  as  it  is  known  among  engineers,  is  the 
gas  obtained  by  the  partial  combustion  of  fuel  in  a  gas 
producer,  and  is  made  by  the  forcing  or  drawing  of  air, 
generally  mixed  with  steam  or  water-vapor,  through  a 
deep  bed  of  fuel  in  a  closed  producer.  An  important  char- 
acteristic of  this  process  is  that  no  external  heat  is  applied 
to  the  producer,  as  in  the  case  of  the  ordinary  gas  retort. 
After  burning  has  once  started  within  the  producer,  the  air 
which  enters  serves  to  keep  up  a  continuous  process  of 
combustion. 

A  simple  gas  producer  is  shown  in  Fig.  38;  A  represents 
the  fire  bars  or  grate,  B  the  air  (and  steam)  inlet,  C  the 
bed  of  fuel,  D  the  hopper  through  which  the  fuel  is  fed, 
and  E  the  gas  outlet. 

Producer  gas  can  be  obtained  from  many  varieties 
of  fuels,  but  those  most  extensively  used  in  this  country 
are  anthracite,  coke,  semi-bituminous  and  bituminous 
coals,  and  lignite.  In  Mexico,  charcoal  and  wood  are  gen- 
erally used,  and  in  Europe  peat  is  becoming  prominent  as  a 
producer  fuel. 

96 


X.     GAS   PRODUCERS 


97 


As  carbon  is  the  most  important  consituent  of  the  fuels 
commonly  used  in  the  manufacture  of  producer  gas,  we  will 
first  assume  this  to  be  the  only  fuel  present,  and  show  the 
action  of  air  alone  on  pure  carbon  in  a  producer.  Of  course 
air  contains  a  certain  percentage  of  nitrogen,  which  is  an 
inert  gas,  and  although  it  affects  the  temperatures  attained, 
we  will  neglect  these  considerations,  and  discuss  simply 
the  action  which  occurs  between  oxygen  and  carbon. 


FIG.  38,— Simple  Gas  Producer. 

(6)  Quantities.  If  the  combustion  in  a  producer  were 
complete,  that  is,  if  the  carbon  were  entirely  oxidized, 
which  would  occur  with  a  shallow  bed  of  fuel  and  an 
abundance  of  air,  the  reaction  would  be  as  follows : 


=  CO2+heat 


(4) 


since  heat  is  liberated  in  this  reaction. 

In  the  actual  producer,  however,  the  attempt  is  made 
to  keep  the  percentage  of  CO2  as  low  as  possible,  since 


98  GAS  POWER 

C02  will  not  ourn  again  in  an  engine  cjdinder,  and  to  form 
a  high  percentage  of  CO,  which  still  has  the  power  of  liberat- 
ing a  large  quantity  of  heat  when  combining  with  oxygen 
to  form  C02- 

This  is  effected  by  maintaining  a  deep  bed  of  carbon 
in  the  producer.  The  resulting  gas  contains  a  large  per- 
centage of  CO,  for  when  there  is  an  excess  of  highly  heated 
carbon,  the  carbon  dioxide  formed  in  the  lower  portion  of 
the  fire,  is  reduced  to  carbon  monoxide  in  the  upper  portion 
according  to  the  equation, 

CO2+C  =  2CO-heat      .....     (5) 

These  two  reactions  probably  do  actually  occur  within 
a  real  producer,  the  first  near  the  bottom  of  the  fuel  bed, 
and  the  second  higher  up.  But,  as  the  ultimate  result 
will  be  the  same  as  though  the  reaction, 

2C+02  =  2CO+heat     .....     (5a) 

occurred  alone,  this  may  be  used  in  making  rough  analyses 
of  producer  operation. 

Equations  expressing  both  the  reaction  and  the  libera- 
tion of  heat  per  pound  of  material  for  the  cases  in  which 
we  are  interested  may  be  written  as  follows: 

C  +  02  =  CO2+  14,600  B.t.u.  per  Ib.  C.    .     .     (6) 
=  2CO+4,500  B.t.u.  per  Ib.  C.     .     .     (7) 
10,100  B.t.u.  per  Ib.  C. 


B.t.u.  per  Ib.  CO    •    ' 

The  first  of  these  gives  the  heat  which  could  be  obtained 
by  burning  the  solid  carbon  to  CO2;  the  second  gives  the 
heat  that  must  be  liberated  in  the  producer  when  CO  is 


X.     GAS  PHODUCEES  99 

formed;    the  third  gives  the  heat  which  could  be  obtained 
by  burning  the  producer  gas  containing  this  CO. 

(c)  Efficiency.     Since   the    calorific   value   of   the   solid 
fuel  is  about  14,600  B.t.u.  per  pound  of  C,  and   of  this 
amount  4500  B.t.u.  are  liberated  in  the  producer  when  CO 
is  formed,  we  have  left  about  10,100  B.t.u.,  as  the  calorific 
value  of  the  gas  which  passes  over  to  the  engine,  to  be  burned. 
By  the  time  this  gas  reaches  the  engine  cylinder,  it  has  been 
cooled  as  a  result  of  having  passed  through  the  various  pieces 
of  scrubbing   apparatus.     Thus   the   ratio   of  the   calorific 
value  of  the  cold  gas  entering  the  engine  to  that  of  the 

original  fuel,  viz.,  -       —  =  69  per  cent,  is  called  the  "  Cold 
14,600 

Gas  Efficiency,"  and  theoretically  is  the  best  that  can  be 
obtained  when  using  air  only. 

Practical  considerations,  however,  serve  to  increase 
the  above  efficiency  so  materially  as  to  make  the  manu- 
facture of  gas  by  this  method  a  paying  commercial  process. 

(d)  Theoretical  Composition.     Assuming  the  action  within 
the  producer  to  occur  according  to  equation  (7),  that  is, 
2C+02  =  2CO,  it  is  obvious  that  2  volumes  of  CO  result 
for  every  volume  of  oxygen  consumed.     The  producer  gas 

79 
would  then  consist  of  2  volumes  of  CO  and  —  XI  or  3.76 

volumes  of  nitrogen. 

The  volume  percentage  of  CO  in  the  gas  would  there- 

2 
fore   be  --  =  34.7  per  cent,  and  the  volume  percentage 


3.76 

of  nitrogen  would  be  =  65.3  per  cent. 

-- 


56.  Necessity  of  Cooling,  and  Methods.  In  the  method 
just  described  of  using  a  dry  air  blast  to  produce  and 
maintain  combustion,  the  temperature  attained  within  the 
producer  must  necessarily  be  very  high,  since  about  4500 
B.t.u.  are  liberated  in  the  fuel  bed  for  every  pound  of  C 


100  GAS  POWER 

burned  to  CO.  This  is  far  more  than  can  be  dissipated 
unless  the  producer  and  the  issuing  gas  attain  a  high  tem- 
perature. Such  high  temperatures  would  result  in  practical 
difficulties  due,  principally,  to  the  rapid  formation  of  clink- 
ers, which  would  seriously  affect  the  operation  of  the 
producer.  To  prevent  or  minimize  this  trouble,  the  com- 
mon practice  is  to  add  a  certain  quantity  of  steam  or  water 
vapor  to  the  air  sent  in.  When  this  steam  passes  over 
highly  heated  carbon,  part  of  it  is  decomposed,  with  the 
absorption  of  an  amount  of  heat  equal  to  that  produced 
by  the  chemical  union  of  its  constituents.  Its  hydrogen 
is  liberated,  and  the  oxygen  combines  with  the  carbon 
to  form  either  CO  or  CO2,  depending  upon  the  temperature 
conditions  under  which  the  reaction  occurs. 

The  following  chemical  equations,  representing  the 
reactions  occurring  when  steam  is  added,  show  that  the 
steam  serves  to  reduce  the  temperature  in  the  producer 
by  absorbing  during  its  decomposition  some  of  the  heat 
liberated  by  the  combustion  of  carbon,  which  heat  would 
otherwise  go  to  raise  the  temperature  of  the  fuel  bed  and  of 
the  issuing  gas.  The  heat  thus  absorbed  is  carried  out 
of  the  producer  in  what  may  be  called  a  potential  or  latent 
form,  since  it  can  be  again  liberated  by  burning  the  products 
of  the  reaction  which  caused  its  absorption,  i.e.,  hydrogen 
and  carbon  monoxide.  The  equations  are: 


H2+CO-heat+heat,  or    .     .     (9) 
H2O+C  =  H2+CO-heat,      .....  (10) 
when  hydrogen  and  carbon  monoxide  result,  and 

2H20+C  =  2H2+CO2-heat+heat,  or     .     (11) 
2H2O+C  =  2H2+CO2-heat,     ....     (12) 
when  hydrogen  and  carbon  dioxide  result. 


X.     GAS  PRODUCEkS  101 

In  both  the  above  cases,  the  formation  of  the  CO  or  CO2 
produces  heat,  but  the  decomposition  of  the  steam  absorbs 
a  much  greater  amount,  and  the  net  effect  is  an  absorption 
of  heat,  with  a  much  lower  temperature  in  the  bed  and  gas. 

Thus  the  steam  not  only  reduces  the  excessive  heat  in 
the  producer,  but  it  also  increases  the  amount  of  com- 
bustible in  the  gas  and  the  calorific  power  per  unit  volume, 
by  replacing  N  with  H  or  with  H  and  CO. 

The  amount  of  steam  employed  depends  upon  the  type 
of  fuel  and  producer  and  the  purpose  for  which  the  gas  is 
to  be  used.  For  average  conditions  in  an  ordinary  pro- 
ducer, 6  per  cent  of  the  weight  of  the  blast  or  10  per  cent 
by  volume  may  be  steam;  sometimes  25  per  cent  more 
steam  may  be  used.  The  quantity  of  steam  required  is 
often  assumed  as  J  to  i  of  the  coal  gasified. 

The  average  theoretical  composition  of  wet-blast  gas 
is  about  CO  =  40  per  cent,  H  =  17  per  cent  and  N  =  43  per 
cent,  and  its  heating  value  per  cubic  foot  is  195.6  B.t.u., 
which  would  indicate  an  efficiency  of  about  93  per  cent. 

Carbon  dioxide  is  sometimes  used  as  a  cooling  agent 
instead  of  steam,  giving  the  following  reaction: 

CO2+C  =  CO+CO-heat (13) 

As  CO2  must  result  when  producer  gas  is  burned,  this 
method  of  cooling  is  effected  by  returning  to  the  producer 
part  of  the  burned  gases  from  the  engine  or  other  consumer. 
This,  however,  also  involves  a  return  of  all  the  nitrogen 
accompanying  this  CO2,  so  that  there  is  more  N  in  the  gas 
issuing  from  the  producer,  and  therefore  a  greater  loss  in 
the  form  of  sensible  heat,  in  the  issuing  gas.  Moreover, 
as  this  sensible  heat  is  not  used  for  the  generation  of  steam, 
for  which  there  is  no  use  in  this  method  of  cooling,  it  cannot 
be  recovered,  and  hence  represents  a  loss.  Cooling  with 
CO2  has,  however,  certain  advantages  when  the  gas  is  to 
be  used  in  a  gas  engine  because  it  produces  a  gas  of  very 


102  GAS   POWER 

uniform  properties  at  all  loads  and  thus  simplifies  the 
operation  of  the  engine,  particularly  with  regard  to  govern- 
ing and  regulation  of  the  time  of  ignition. 

57.  Types  of  Producers.  The  various  real  producers 
used  to  carry  out  the  processes  which  have  just  been  outlined 
are  divisible  into  types  in  several  different  ways.  The  most 
common  division  is  based  on  direction  of  draft  through  the 
producer  and  the  way  in  which  that  draft  is  created.  Exam- 
ples will  be  given  in  subsequent  paragraphs. 

Another  method  of  classification  is  on  the  basis  of  fuel 
utilized;  thus  there  are  hard  coal  producers,  bituminous 
or  soft  coal  producers,  peat  producers,  and  such. 

Again,  the  method  used  for  supporting  the  fuel  column 
is  often,  used  as  a  basis  for  classification.  Thus  there  are 
grate-bottom  producers  in  which  this  column  is  supported 
on  a  grate  of  some  sort,  and  there  are  water-bottom  pro- 
ducers in  which  the  fuel  column  rests  on  a  pile  of  its  own 
ash  contained  in  a  water-filled  saucer  in  the  floor  of  the 
producer  house. 

These  and  other  classifications  will  be  better  appreciated 
after  a  study  of  the  description  of  producers  which  follows: 

(a)  Suction  Producers. 

In  Fig.  39  is  shown  a  typical  suction  producer  as  made 
by  Fairbanks,  Morse  and  Company.  The  name  of  suction 
producer  is  applied  to  all  plants  in  which  the  draft  through 
the  producer  is  created  by  the  suction  of  the  engine.  The 
plant  shown  would  be  completely  described  by  calling  it 
an  updraft,  grate-bottom,  suction  producer.  Its  method  of 
operation  should  be  evident  from  the  figure. 

Such  producers  as  are  here  shown  are  well  fitted  for  the 
gasification  of  such  fuels  as  anthracite  coal  and  coke,  but 
unless  considerably  modified  they  cannot  be  used  with 
fuels  high  in  volatile  material  for  reasons  which  are 
indicated  in  the  following  paragraphs. 


X.     GAS  PRODUCERS, 


GAS  POWER 


FIG.  40  (a).— R.  D.  Wood  Pressure  Producer. 


X.      GAS   PKODUCERS 


105 


They  are  ideally  simple,  comparatively  cheap,  and  easy 
to  operate  when  properly  designed.  They  are  built  in 
sizes  ranging  from  about  ten  to  several  hundred  horse- 
power, the  rating  being  based  on  the  engine  horse-power 
which  they  can  supply.  With  average  fuels  it  is  generally 
safe  to  figure  on  a  consumption  of  from  1  to  1.2  pounds  of 
fuel  per  brake-horse-power  hour,  and  better  figures  have 
been  obtained  in  manv  instances. 


(6)  Pressure  Producers. 

In  Fig.  40  (a)  is  shown  a  section  of  a  pressure  producer 
manufactured  by  R.  D.  Wood  &  Co.  All  producers  in 
which  the  draft  is  created  by  some 
form  of  blower  which  raises  the 
pressure  at  the  entering  side  or  end 
of  the  fuel  column  are  called  pressure 
producers.  This  is  usually  done  by 
means  of  a  steam  jet  blower  desig- 
nated by  6  in  the  figure  and  shown 
in  greater  detail  in  Fig.  40  (6).  A 
fairly  complete  description  of  the 
producer  here  shown  would  be  given 
by  calling  it  an  updraft,  grate-bottom 
pressure  producer. 

The  particular  type  illustrated  is 
furnished  with  an  automatic  feed 
and  a  rotating,  self-cleaning  ash 
table.  Both  of  these  devices  serve 
to  maintain  approximately  constant 
conditions  and  hence  constant  com- 
position of  the  gas.  They  are  often 
used,  in  one  form  or  another,  on  the 
larger  producers. 

The     updraft,     pressure     type     is 
limited  with  regard  to  the  character  of  fuel  in  much  the 


FIG.  40  (6). 
Steam  Blower. 


106  GAS   POWER 

same  way   as    is    the    updraft    suction    producer,    as    will 
appear  in  the  paragraphs  immediately  following. 

(c)  Modifications  of  the  Producer  for  Different  Fuels. 

In  the  elementary  discussion  it  was  assumed  that  pure 
carbon  only  was  used  in  the  producer  for  the  manufacture 
of  gas  and  the  various  chemical  changes  were  calculated 
on  this  assumption.  However,  in  practice  wa  find  that 
actual  fuels  contain  other  constituents  than  carbon,  and 
when  heated  give  off  more  or  less  volatile  material.  Each 
fresh  charge  is  heated  and  subjected  to  this  process  of  dis- 
tillation before  it  descends  into  the  zone  where  partial 
combustion  occurs. 

Thus  in  an  updraft  producer  we  obtain  a  mixture  of  the 
volatile  substances  that  are  distilled  off,  and  of  the  gas 
resulting  from  the  residue  which  is  left  after  the  raw  fuel 
has  been  more  or  less  completely  deprived  of  its  volatile 
constituents  by  the  action  of  heat. 

These  volatile  constituents  consist  partly  of  gases  and 
partly  of  condensible  vapors.  The  latter,  if  allowed  to 
pass  out  with  the  gas,  must  generally  be  condensed  and 
separated  from  the  producer  gas  before  it  can  be  used  in  a 
gas  engine.  In  the  case  of  fuels  like  anthracite,  which  con- 
tain little  volatile  material,  no  difficulty  is  met  from  this 
source,  but  in  the  case  of  fuels  rich  in  oxygen  and  hydrogen, 
as  bituminous  or  semi-bituminous  coals,  lignite,  peat,  etc., 
the  thermal  efficiency  of  the  producer  gas  process  may  be 
decreased  from  12  to  20  per  cent  by  the  removal  of  the 
tarry  vapors  from  the  gas. 

To  prevent  this  loss,  which  is  inevitable  if  such  fuels 
are  gasified  in  the  simple  type  of  apparatus  already  described, 
producers  are  also  arranged  to  burn  the  tarry  vapors  in  the 
producer  itself  or  decompose  or  convert  them  into  com- 
bustible gases  which  will  not  condense  at  ordinary  temper- 
atures. 


X.     GAS   PRODUCERS  107 

(d)  Downdraft  Producers. 

Producers  operating  on  the  "  downdraft  "  principle  were 
early  tried  as  a  means  of  fixing  the  tarry  vapors.  These 
were  fairly  successful,  and  had  the  advantage  of  doing 
away  with  all  smoke  during  the  charging  of  the  coal. 

One  of  the  best-known  American  types  of  downdraft 
producer  is  the  Loomis-Pettibone,  shown  in  Fig.  41.  The 
plant  consists  of  the  producer  or  generator,  an  economizer, 
a  wet  and  a  dry  scrubber,  an  exhauster  and  a  gas  holder. 

Coal  is  charged  through  the  doors  at  the  top  as  shown 
at  m  into  the  annular  space  between  the  air  inlet  nozzle 
and  the  firebrick  lining. 

Air  enters  the  economizer  at  b  around  the  pipe  e  through 
which  the  hot  gases  are  drawn  from  the  producer.  It  is 
heated  by  passing  over  the  tubes  e'  and  t,  and  is  mixed  with 
the  steam  which  results  from  the  water  entering  through  d 
and  being  vaporized  as  it  trickles  down  the  outside  of  the 
central  tube  e',  the  function  of  which  is  that  of  a  flash  boiler. 
The  air  and  steam  then  pass  over  into  the  drum  /  and  down 
through  the  fuel  bed  and  grate  A  and  through  the  pipe  e 
because  of  the  suction  produced  by  the  exhauster  C.  The 
hot  gases  next  pass  through  the  wet  scrubber  B,  where  they 
are  cooled  and  exhausted  into  the  dry  scrubber  D,  which 
still  further  cleans  and  dries  the  gases,  after  which  they 
pass  into  the  gas  holder  E. 

The  amount  of  gas  in  the  holder  E  is  regulated  automat- 
ically by  means  of  a  by-pass  not  shown.  A  wire  rope 
connects  the  top  of  the  holder  to  valves  so  located  that 
when  the  holder  is  full  of  gas  and  in  its  top  position  the 
exhauster  simply  pumps  its  discharge  back  into  its  own 
suction  through  the  by-pass.  As  the  holder  drops,  the  by- 
pass is  gradually  shut  off  so  that  the  exhauster  draws  on 
the  producer. 

When  starting  up,  the  valve  k  is  closed  and  the  valve 
h  is  opened,  so  that -the  exhauster  can  discharge  to  the 


108 


GAS   POWER 


X.     GAS  PRODUCERS  109 

atmosphere  through  the  purge  pipe  p  until  the  gas  made 
is  of  such  quality  that  it  can  be  sent  to  the  holder. 

Whenever  the  fuel  bed  becomes  stopped  up  with  clinkers, 
etc.,  the  valve  between  the  economizer  and  wet  scrubber 
is  closed  and  high-pressure  gas  is  forced  up  through  the 
grate  A,  breaking  up  the  fuel  bed  thoroughly. 

Any  fuel  containing  large  amounts  of  volatile  matter,  as 
bituminous  coal,  wood,  etc.,  can  be  successfully  gasified 
in  this  producer.  All  the  gases  and  tarry  matter  distilled 
from  the  fresh-fuel  magazine  are  mixed  with  air,  and  partly 
burned  and  partly  "  cracked  "  as  they  pass  downward 
through  the  bed  of  incandescent  fuel  from  which  they  issue 
as  fixed  or  non-condensible  combustible  gases.  In  starting 
this  producer,  a  bed  of  incandescent  coke  or  similar  material 
is  first  built  upon  the  grate.  This  bed  serves  to  fix  the 
tarry  vapors  distilled  off  from  the  first  coal  supplied. 

Since  all  the  ash  which  does  not  fall  through  the  brick 
arch  must  remain  within  the  fuel  column,  the  producer 
does  not  permit  of  continuous  operation.  In  practice  it 
is  found  that  the  accumulation  of  ash  generally  necessitates 
shutting  down  and  completely  cleaning  about  once  a  week. 

In  Fig.  42  is  shown  a  section  of  the  Ackerlund  Bituminous 
Gas  Producer,  which  is  distinguished  by  being  one  of  the 
first  successful  downdraft  producers  to  permit  of  continuous 
operation. 

The  principal  parts  of  the  apparatus  and  the  method 
of  operation  are  clearly  shown  in  the  figure,  the  distinguish- 
ing feature  being  the  water  bottom  which  makes  it  possible 
to  operate  continuously. 


110 


GAS  POWER 


X.     GAS  PRODUCERS 


111 


(I)  Double-zone  Producers. 

The  Westinghouse  Producer  for  bituminous  fuels   and 
lignite  shown  in  Fig.  43  is  of  the  double-zone  type. 


FIG.  43. — Westinghouse  Double-zone  Producer. 

About  the  center  of  the  producer  is  a  hollow  annular 
casting,    called  the  vaporizer,   which  is   kept  nearly  filled 


112  GAS  POWER 

with  water.  The  hot  gases  drawn  from  the  top  and  bottom 
beds  pass  under  this  casting  and  vaporize  the  water.  Air 
enters  through  the  pipe  a  and  circulates  over  the  surface 
of  the  hot- water  in  the  vaporizer,  mixing  with  the  steam, 
and  passing  off  through  the  pipes  on  the  left  to  the 
top  and  bottom  fuel  beds,  to  effect  combustion.  The 
amount  is  regulated  by  means  of  the  valves  c  and  c'  in 
the  pipes. 

There  is  no  grate  in  this  producer,  the  bottom  being 
submerged  in  a  water  seal  formed  by  a  basin  in  the  con- 
crete foundation.  Ash  and  clinkers  can  be  removed  easily 
through  the  opening  bet\veen  the  bottom  of  the  producer 
shell  and  the  bottom  of  the  water  basin. 

It  will  be  observed  that  the  upper  part  of  this  apparatus 
is  merely  a  downdraft  producer  with  its  own  incandescent 
zone,  in  which  the  vapors,  distilled  from  the  fuel  fed  in  on 
top,  are  fixed.  The  coke  formed  in  this  upper  zone  works 
downward  and  ultimately  becomes  the  fuel  gasified  in  the 
updraft  producer,  which  forms  the  lower  part  of  the 
apparatus. 

58.  Cleaning  Apparatus.  When  producer  gas  is  burned 
in  furnaces  used  in  metallurgical  processes,  impurities, 
such  as  tar,  dust  and  ashes,  do  not,  in  general,  prevent 
its  successful  utilization.  Therefore  expensive  gas-cleaning 
equipment  is  unnecessary,  and  the  gases  reach  the  furnace 
at  a  high  temperature,  resulting  in  an  increased  efficiency, 
because  of  the  retention  of  sensible  heat  and  the  tarry 
vapors  which  are  easily  burned,  thereby  adding  materially 
to  the  total  quantity  of  heat  derived. 

When,  however,  the  gas  is  to  be  used  in  an  engine,  it 
is  absolutely  necessary  to  remove  all  tarry  products  which 
would  collect  in  the  valves  and  in  the  passages  leading  to 
the  engine,  and  all  dust  and  grit  which  would  score  the 
cylinder  walls.  Therefore  the  gas  must  be  thoroughly 
cleaned,  and,  incidentally,  cooled  before  entering  the 
engine.  The  most  common  process  for  removing  the 


X.      GAS  PRODUCERS  113 

impurities  is  called  scrubbing  and  ordinary  forms  of  wet 
and  dry  scrubbers  are  shown  in  Fig.  41. 

In  the  wet  scrubber,  the  hot  gases  enter  at  the  bottom 
and  pass  upward  through  a  bed  of  coke  or  other  convenient 
material,  over  which  water  is  sprayed.  The  water  and 
gas  thus  come  into  intimate  contact,  the  particles  of  dust 
are  washed  out  and  the  tarry  vapors  are  condensed  and 
removed.  The  gas  is  cooled  and  passed  on  through  dry- 
scrubbers  containing  excelsior  or  through  other  water  sepa- 
rators, for  the  purpose  of  removing  the  excess  moisture 
and  remaining  traces  of  dust  and  tar. 

For  bituminous  coals,  lignite,  peat  and  other  tarry 
fuels  in  updraft  producers,  the  above  scrubbing  process  is 
not  alone  sufficient,  so  mechanical  tar  extractors  are  often 
used.  The  chief  disadvantages,  however,  of  this  method 
are  loss  of  heat  value  due  to  the  removal  of  the  tar  from  the 
gas,  the  loss  of  power  required  to  operate  the  tar  extractors, 
and  the  fact  that  the  tar  is  a  disagreeable  substance  to 
handle  around  a  plant  and  often  difficult  to  dispose  of. 

59.  Blast-furnace  as  Gas  Producer.  The  blast  furnace 
is  one  of  the  most  common  types  of  gas  producer,  although 
not  built  primarily  for  this  purpose,  the  gas  being  a  by- 
product. 

In  making  pig  iron  from  ore,  coke,  or  anthracite  coal, 
iron  ore  and  limestone  or  similar  flux  are  charged  so  as  to 
form  a  deep  bed  within  the  furnace.  This  may  be  regarded 
as  nothing  more  than  a  bed  of  fuel  with  an  extremely  high 
ash  content,  and  the  blast  of  air  introduced  at  the  bottom 
of  the  furnace  causes  the  formation  of  producer  gas  in 
practically  the  same  way  as  occurs  in  an  ordinary  updraft 
producer. 

The  gas  given  off  has  a  low  heating  value,  averaging, 
generally,  from  80  to  90  B.t.u.  per  cubic  foot,  but  occasion- 
ally running  over  100. 

The  cleaning  apparatus  must  be  large  and  expensive, 
due  to  the  large  amount  of  dust  carried  by  the  gas.  But 


114  GAS   POWER 

even  with  the  high  cost  of  cleaning  it  is  found  economical 
to  use  this  by-product,  which  would  otherwise  be  wasted. 

The  most  notable  installations  in  this  country  are  those 
at  the  Lackawanna  Steel  Company's  plant  at  Buffalo, 
N.  Y.,  and  the  Indiana  Steel  Company's  plant  at  Gary,  Ind. 
The  former  develops  40,000  h.p.  by  means  of  2-cycle  gas 
engines  in  units  of  1000  and  2000  h.p.,  and  the  latter  con- 
sists of  17  units  of  2000  kw.  rating  each,  and  16  blowing 
engines  of  about  the  same  capacity.  Six  new  units  of  3000 
kw.  each  have  recently  been  ordered  and  are  being  installed. 

Experience  has  shown  that  after  all  the  necessary  gas 
has  been  used  for  heating  the  hot  blast  and  operating  the 
gas-driven  blowing  engines  there  still  remains  enough  gas 
to  produce  about  3000  h.p.  continuously  for  ever}'  100  tons 
of  pig  iron  made  per  twenty-four  hours. 


CHAPTER  XI 


CLASSIFICATION  AND  TYPES  OF  MODERN  ENGINES 

60.  Multiplicity  of  Classifications.  The  various  types 
of  modern  internal  combustion  engines  may  be  classified 
according  to  the  following: 


(1)  As  to  cycle, 


(3)  As  to  fuel  used , 


(4)  As  to  use , 


(5)  As  to  position  of  axis .  .  . 

(6)  As  to  action 


(2)  As  to  method  of  operation. 


(a)  Otto 
(6)  Diesel 

(c)   Intermediate 

(a)  Two-stroke 
(6)   Four-stroke 


(a)  Gasoline 
(6)   Kerosene 


(c)   Gas 


(d)  Oil. 


(  (1)  Illuminating 

(2)  Natural 

(3)  Producer 

(4)  Blast-furnace 
Kerosene,  through  all  the 

intervening  distillates 
to  crude  oil 


(a)  Stationary 

(6)   Portable 
j    (c)   Automobile 
j    (d)  Marine 
I  (e)   Aeroplane 

(a)  Vertical 
(6)  Horizontal 
(c)   Inclined 

(a)  Single  acting  (trunk  piston) 
(6)   Double  acting 

115 


(7)  As  to  cylinder  arrangement    - 


116  GAS  POWER 

(a)  Twin  (2  parallel  cylinders  with 
separate  frames) 

(6)  Multicylinder  engine  2,  3,  etc., 
to  any  number  of  parallel  cyl- 
inders with  combined  frame 

(c)  Tandem  (2  co-axial  cylinders  on 

same  side  of  crank  shaft) 

(d)  Opposed  (2  co-axial  cylinders  on 

opposite  sides  of  crank  shaft) 

,o\    >  •  (  (a)  Hit-and-miss 

(8)  As  to  governing <    ;  ' 

I  (6)   Throttling,  etc. 

61.  Division  on  Basis  of  Fuel  Used.  Engines  operating 
on  illuminating  gas  are  built  in  sizes  from  2  to. about  160 
developed  horse-power  (d.h.p.)  per  cylinder,  per  end,  and 
these  may  be  considered  as  the  limits  for  engines  using 
this  type  of  gas,  although,  because  of  its  high  cost,  this 
gas  is  seldom  used  in  engines  larger  than  50  h.p.  in  this 
country.  There  is  on  record,  however,  a  42"X60",  double- 
acting,  twin-tandem,  horizontal  engine,  88  r.p.m.,  built 
by  the  Snow  Steam  Pump  Company,  using  illuminating 
gas  and  rated  at  4000  d.h.p.  total,  which  means  500  d.h.p. 
per  cylinder  end.  This  engine  was  installed  to  meet  very 
peculiar  conditions. 

For  engines  operating  on  natural  gas  the  limits  of  sizes 
as  built  in  America  to-day  are  from  about  2  to  about  625 
d.h.p.  per  cylinder  per  end.  For  single-acting  engines  of 
this  type,  the  upper  limit  runs  from  180  to  200  d.h.p.  per 
cylinder  per  end.  Typical  dimensions  of  double-acting, 
tandem,  horizontal  engines  operating  on  natural  gas  are  from 
11"X12"  to  43"X60",  developing  horse-powers  from  60 
total  or  15  per  cylinder  end,  to  2500  total  or  625  per  cylinder 
end,  the  corresponding  speeds  varying  from  250  to  90  r.p.m. 

For  engines  operating  on  producer  gas  the  average  limits 
of  sizes  as  built  in  America  to-day  are  from  1J  to  200  or  250 
d.h.p.  per  cylinder  per  end.  Exceptions  to  these  sizes 
again  are  found  in  double-acting  engines  built  by  various 


XI.     CLASSIFICATION  AND  TYPES  OF  ENGINES       117 

companies  ranging  from  12J"X12"  to  48"X60"  and 
developing  60  total  h.p.  or  15  per  cylinder  end,  to  2500 
h.p.  total  or  625  per  cylinder  end,  with  corresponding 
r.p.m.  of  250  to  90. 

Engines  operating  on  blast  furnace  gas  are  built  in 
sizes  from  100  d.h.p.  up  to  about  500  d.h.p.  per  cylinder 
end.  Typical  dimensions  of  the  larger  sizes  as  installed  in 
several  of  the  steel  plants  are  30"X42"  twin-tandem, 
double-acting,  developing  1500  h.p.  total  or  187.5  per 
cylinder  end;  42//X60//  and  42"XSO"  engines  for  gas- 
blowing  purposes;  a  42"X70"  twin-tandem,  developing 
3600  h.p.  total  or  450  h.p.  per  cylinder  end;  a  44"X60" 
twin-tandem,  double-acting,  at  83.3  r.p.m.,  developing 
about  4000  h.p. 

Gasoline  engines  are  built  in  sizes  from  \  h.p.  to  60  h.p. 
per  cylinder  end,  while  a  few  are  built  up  to  90  h.p.  or  over. 
Single-acting,  horizontal,  single-cylinder  engines  up  to 
22"X28",  developing  125  h.p.  per  cylinder  end  at  150 
r.p.m.  have  been  installed.  Because  of  the  high  cost  of 
this  fuel,  such  engines  are  usually  bought  only  when  special 
conditions  are  to  be  met. 

Kerosene  and  heavy  oil  engines  operating  on  the  Otto 
cycle  are  built  in  sizes  ranging  from  2  h.p.  to  125  h.p. 
per  cylinder  end.  Typical  dimensions  of  this  type  run 
from  5|"X10",  developing  7  h.p.,  to  14//X24//,  developing 
90  h.p.,  operating  on  the  California  distillates.  The  Diesel 
engine  is  now  often  built  in  sizes  even  as  large  as  225  h.p. 
per  cylinder  end,  and  three  cylinder  units  are  very  common 
for  stationary  work.  Diesel  engines  are  seldom  built 
smaller  than  10  h.p.  per  cylinder  per  end.  Recent  experi- 
mental work  by  European  firms  indicates  the  possibility  of 
obtaining  1000  to  1500  h.p.  per  double-acting,  two-stroke, 
cylinder. 

62.  Division  on  Basis  of  Use.  Under  this  heading 
we  may  divide  internal  combustion  engines  into  four  classes: 
(1)  Stationary  engines,  or  those  which  are  used  exclusively 


118  GAS  POWER 

in  "  power  plants,"  as  for  electric  lighting,  pumping,  operat- 
ing machine  shops,  manufacturing  plants,  etc.  These 
may  vary  in  size  from  the  smallest  to  the  largest  tandem 
and  twin-tandem  engines  mentioned  above  and  with  few 
exceptions  operate  on  the  four-stroke  principle. 

(2)  Portable  engines,  which  are  built  only  in  the  smaller 
sizes  to  be  easily  and  quickly  transported  as  on  trucks, 
road  rollers,  traction  engines,  etc.,  from  place  to  place  or 
used   for   various   purposes   about   a   farm.     Gasoline   and 
kerosene  engines  of  this  type  and  adapted    especially  to 
farm  use  are  finding  a  tremendous  field,  and  the  industry 
is  rapidly  becoming  a  large  one. 

(3)  Automobile  or  Auto  engines,  which  were  developed 
primarily  for  use  in  the   gasoline   automobile.     They   are 
almost  exclusively  built   in  four,  and   six-cylinder  vertical 
units,  and  most  of  them  operate  on  the  four-stroke  principle. 
There  are,  however,  a  few  notable  exceptions  to  the  last 
statement. 

The  auto  type  is  now  being  extensively  applied  to  heavy 
truck  and  tractor  work,  to  high-powered  fire  engines,  and  to 
a  number  of  allied  uses.  It  has  also  found  extensive  applica- 
tion in  small  and  medium-powered,  high-speed  motor  boats. 

(4)  Marine  engines,  which  are  similar  in  general  construc- 
tion to  the  auto-engine,  save  that  in  small  units  we  find  the 
two-stroke  type  widely  used   in  the   motor-boat  industry, 
because  of  its  simplicity,  cheapness,  and  ease  of  operation. 
For  larger  motor  boats  and  launches,  etc.,  the  four-stroke 
vertical  engine  in  one-,  two-,  three-  and  four-cylinder  units, 
is    common,    because    of    the    more    severe    requirements, 
necessitating  durability,  reliability,  and  speed. 

The  modern  Diesel  oil  engine  is  now  being  installed 
abroad  in  almost  every  type  of  vessel,  and  bids  fair  to  rival 
steam  for  marine  use,  because  of  the  higher  powers  to  be 
obtained  for  the  space  now  occupied  by  a  steam  plant,  the 
elimination  of  boilers,  and  the  reduction  in  space  required 
to  carry  the  fuel  oil. 


XI.     CLASSIFICATION  AND  TYPES  OF  ENGINES      119 

Irrespective  of  fuel  and  type,  sizes  from  1  to  25  h.p. 
are  suitable  for  the  various  types  of  small  motor  boats; 
those  from  25  to  100  or  more  horse-power  for  larger  boats 
and  small  yachts;  and  those  up  to  1000  h.p.  for  small 
cruisers,  tugs,  ferry-boats,  torpedo-boats  and  destroyers. 
Marine  motors  are  generally  of  heavier  construction  than 
the  corresponding  auto-engine,  because  of  the  wear  and 
tear  incident  to  continuous  operation  under  full  power, 
which  is  seldom  required  of  an  automobile  engine. 

(5)  A  fifth  type  may  be  mentioned,  namely  the  aero- 
type  motor,  which  has  been  but  recently  developed,  to  meet 
the  requirements  of  great  strength  and  reliability,  very 
light  weight  and  high  speed,  necessitated  by  this  particular 
industry. 

63.  Mechanical  Construction.  To  summarize  briefly 
the  leading  features  of  engine  design,  with  their  advantages 
and  disadvantages,  we  may  say  that  small  engines,  almost 
without  exception,  are  built  single-acting,  and  when  more 
power  is  required,  the  number  of  cylinders  is  increased. 
The  single-acting  engine,  either  vertical  or  horizontal, 
has  the  obvious  advantage  of  great  simplicity  of  manufacture 
and  therefore  small  first  cost. 

The  trunk  piston  with  its  obvious  disadvantages,  which, 
however,  can  be  overcome  successfully  in  the  smaller  and 
intermediate  sizes,  is  used  almost  exclusively,  thereby 
obviating  the  necessity  of  the  crosshead  and  guides,  ex- 
pensive water-cooled  pistons,  and  piston-rods,  etc.  For 
large  machines  the  trunk  piston  (without  crosshead)  is 
practically  impossible,  because  of  the  great  weight  to  be 
supported,  the  necessity  of  obtaining  accurate  fits  to  prevent 
leakage  of  gases  past  the  piston,  the  difficulty  of  proper 
lubrication,  and  such. 

Medium  sizes,  from  one  to  several  hundred  horse-power, 
are  commonly  built  single-acting  with  cylinders  in  tandem 
and  pistons  and  rods  supported  by  crossheads,  but  all  the 
larger  sizes  are  built  double-acting,  with  two  cylinders  in 


120  GAS   POWER 

tandem.  This  arrangement  is  "  twinned  "  for  the  largest 
powers. 

Much  can  be  said  with  regard  to  the  relative  advantages 
and  disadvantages  of  horizontal  and  vertical  engines. 
Small  engines  are  commonly  built  both  horizontal  and 
vertical,  often  by  the  same  manufacturer.  The  vertical 
type  has  the  advantage  of  a  smaller  and  lighter  founda- 
tion, as  well  as  of  allowing  a  more  uniform  lubrication  of 
the  cylinders.  It  is  also  claimed  that  the  wear  on  the 
cylinder  wall  is  less  in  the  case  of  the  vertical  machine. 
The  box  frame  with  enclosed  crank  case,  using  splash 
lubrication,  affords  a  cheap  construction  and  simple  but 
satisfactory  lubrication  and  is  a  favorite  form  with  this 
type  of  engine. 

In  the  medium  and  larger  sizes  of  vertical  machines 
there  are  the  additional  advantages  of  being  able  to  dis- 
mount them  more  easily  than  the  horizontal  type  by  means  of 
the  overhead  crane,  and  the  fact  that  vertical  constructions 
occupy  less  floor  space  than  do  horizontal  engines  of  like 
power.  The  commercial  limit  to  the  size  of  vertical  engines 
has  been  set  principally  by  the  difficulties  met  in  attempting 
to  make  them  double-acting  and  thus  increasing  the  power 
per  cylinder  and  per  unit  of  weight.  The  chief  difficulty 
is  that  of  getting  a  satisfactory  location  of  the  valves  for 
the  lower  end  of  the  cylinder. 

The  horizontal  machine  has  the  advantage  of  being  more 
easily  handled  and  operated,  since  all  climbing  and  mount- 
ing of  platforms,  excepting  in  the  largest  sizes,  are  obviated. 
Also,  the  operator  can  watch  his  machine  more  closely, 
as  all  parts  are  practically  on  one  level.  Itjs  also  easier, 
in  the  case  of  horizontal  engines  using  artificial  power  gases, 
which  contain  a  certain  amount  of  dust,  to  pass  this  through 
and  out  of  the  cylinder  than  is  the  case  in  a  vertical  machine, 
since  the  exhaust  valve  can  be  located  at  the  bottom  of 
the  cylinder. 

The  cylinder  arrangement  varies   according  to  the  sizes 


XI.     CLASSIFICATION  -AND  TYPES  OF  ENGINES      121 

of  engines  employed  and  the  requirements  of  the  service. 
In  the  small  and  intermediate  sizes  of  vertical  engines,  as 
mentioned  above,  the  power  may  be  increased  by  placing 
two,  three,  or  more  cylinders  on  the  same  shaft,  which  is 
termed  multi-cylinder  construction. 

In  horizontal  engine  practice  two  cylinders  may  be 
placed  side  by  side  on  separate  frames  (known  as  "  twin 
arrangement  "),  or  they  may  be  fastened  together  in  "  tan- 
dem," which  would  necessitate  only  one  connecting  rod. 
Two  tandems  may  be  placed  together  in  parallel  and  con- 
nected to  the  same  crank  shaft,  giving  what  is  known  as  a 
"  twin-tandem  "  engine.  In  small  sizes  a  duplex  arrange- 
ment is  sometimes  used,  two  cylinders  being  placed  side 
by  side  and  fastened  to  the  same  frame. 

When  two  cylinders  are  placed  horizontally  on  opposite 
sides  of  a  main  shaft  with  the  connecting  rods  fastened  to 
the  same  or  adjacent  crank  pins,  the  arrangement  is  known 
as  "  two-cylinder  opposed."  This  may  be  duplicated  to 
form  a  "  four-cylinder  opposed "  type.  The  opposed 
arrangement  is  no  longer  used  except  for  the  small 
sizes;  it  is  favored  at  the  present  time  by  some  tractor 
manufacturers  because  of  the  automatic  balance  which 
it  gives. 

The  advantage  of  one  type  over  another  depends  upon 
the  class  of  work  for  which  it  is  to  be  used,  the  relative  cost, 
the  floor  space  and  head-room  available,  the  type  of  fuel, 
character  of  attendance,  and  a  number  of  other  considera- 
tions. 


CHAPTER    XII 
MODERN    TYPES    OF    GAS    AND    GASOLINE    ENGINES 

64.  The  Pierce  Arrow  Automobile  Engine.  This  engine 
is  built  by  the  Pierce  Arrow  Motor  Car  Company,  for  use 
in  the  cars  of  the  same  name.  It  is  shown  in  Figs.  44  (a), 
(6)  and  (c).  The  first  figure  gives  a  longitudinal  section 
along  the  centre  line  of  the  engine,  the  second  a  vertical 
cross-section  through  the  centre  of  the  cylinder  which 
is  shown  at  the  left  in  Fig.  44  (a),  and  the  third  is  a  part 
elevation  and  part  section.  The  engine  is  built  with  six 
cylinders,  cast  together  in  pairs,  so  that  there  are  three  units 
per  engine.  As  shown  in  Fig.  44  (6),  these  cylinders  are 
of  the  "  T-head  "  type,  the  admission  valve  A  and  the 
exhaust  valve  E  being  carried  in  pockets  opening  off  of  the 
clearance  space. 

The  combustible  mixture  is  supplied  by  the  carbureter  C 
through  the  inlet  manifold  7,  and  the  burned  gases  are 
discharged  through  the  exhaust  manifold  M.  The  car- 
bureter is  fitted  with  a  warm- water  jacket  supplied  through 
P  from  the  jacket  system  of  the  engine,  so  that  vaporiza- 
tion of  the  fuel  may  be  assisted  in  cold  weather. 

The  valves  are  operated,  as  shown  in  Fig.  44  (b),  by  two 
cam  shafts  S  and  Sr  gear-driven  from  the  crank  shaft. 

Two  separate  ignition  systems  are  provided.  One  is 
operated  by  a  battery,  and  is  connected  to  the  plugs  D. 
It  is  controlled  by  the  timer  T,  which  is  gear-driven  from 
the  inlet  shaft.  The  other  system  is  operated  by  a  high- 
tension  magneto  and  is  connected  to  the  plugs  F.  The 

122 


XII.     TYPES  OF  GAS  AND  GASOLINE   ENGINES     123 


124 


GAS  POWER 


PIG.  44  (6). — Pierce- Arrow  Automobile  Engine,  Vertical  Section. 


XII.     TYPES  OF  GAS  AND   GASOLINE  ENGINES     125 

systems  can  be  used  separately  or  both  can  be  used  at  the 
same  time. 

The  location  of  the  plugs  in  the  inlet  cavity  assures 
their  points  being  scrubbed  by  the  incoming  mixture, 
thus  keeping  them  free  of  oil  and  carbon.  It  also  insures 
the  presence  of  pure,  and  therefore  readily  ignitable,  mixture 
in  their  immediate  neighborhood. 

The  cooling  water  is  circulated  by  a  small  centrifugal 
pump  which  is  gear-driven  from  the  exhaust  cam-shaft 


Oil  Gauge  on  Dash. 


.Drain-Cock 


Oil  Pump 


FIG.  44  (c). — Part  Section  of  Fierce-Arrow  Automobile  Engine. 

system.  This  pump  receives  cooled  water  from  the  radiator, 
forces  it  through  the  jackets,  and  through  the  pipe  G  in 
Fig.  44  (a),  back  to  the  radiator.  The  fan  shown  in 
the  same  figure  is  driven  by  a  belt  from  the  crank  shaft. 
It  serves  to  assist  the  circulation  of  air  through  the  radiator 
and  about  the  cylinders  of  the  engine  and  thus  assists  in 
the  cooling. 

i  Lubrication  is  forced  by  a  small  pump  as  shown  in  Fig. 
44  (c).  The  oil  is  delivered  to  the  main  bearings  and  travels 
through  drilled  holes  in  the  shaft  to  the  crank  pins.  The 


126 


GAS  POWER 


wrist  pins  are  lubricated  by  oil  carried  "fronx  the  crank  pin 
by  means  of  a  small  pipe  fastened  to  the  connecting  rod  as 
shown. 

The  engine  can  be  started  by  a  hand  crank  in  the  ordinary 
way,  or  by  high-pressure  air  which  is  controlled  from  the 
seat.  This  air  is  prepared,  while  the  engine  is  in  operation, 
by  a  small  four-cylinder  pump  under  the  control  of  the 
operator  and  is  stored  in  a  tank. 


FK;.  45  (a). — Side  Elevation  of  Fairbanks-Morse  Marine  Engine. 


65.  The  Fairbanks-Morse  Marine  Engine.  The  engine 
illustrated  in  Figs.  45  (a),  (6)  and  (c)  and  described  in  the 
following  paragraphs  is  one  of  several  types  of  marine 
engines  marketed  by  Fairbanks,  Morse  &'  Co.  It  is  a 
single-cylinder,  single-acting  engine,  operating  on  the  two- 
stroke  principle  and  using  crank-case  compression.  Because 
of  the  number  and  arrangement  of  the  ports,  which  are 


XII.     TYPES  OF  GAS  AND  GASOLINE  ENGINES     127 

controlled  by  the  piston,  it  is   further   known  as  a  three- 
port  engine. 

Starting  the  description  of  the  method  .of  operation  with 
the  piston  in  the  position  shown  in  Fig.  45  (c),  the  burned 
gases  of  the  expansion  which  has  just  been  completed  are 
passing  out  through  the  exhaust  port,  and  the  new  charge, 
which  was  compressed  in  the  crank  case,  during  the  down- 


rfti 


FIG.  45  (6). — End  Elevation  of  Fairbanks-Morse  Marine  Engine. 

stroke,  is  passing  into  the  cylinder  through  the  inlet  or 
transfer  port.  During  the  next  up-stroke,  this  charge, 
mixed  with  such  burned  gases  as  remain  in  the  cylinder,  is 
compressed.  It  is  then  burned  at  about  the  end  of  the  stroke 
and  expands  on  the  next  down-stroke,  thus  completing  the 
working  cycle. 

During  the  up-stroke,   a  partial  vacuum  is  created  in 
the  crank  case  until  the  piston  uncovers  the  third  port. 


128 


GAS  POWER 


When  this  occurs,  air  rushes  through  the  carbureter  and 
this  port  into  the  crank  case,  where  it  is  compressed  by  the 
returning  piston. 

In  engines  of  this  type,  difficulty  is  often  experienced 
because  of  back  fires,  or  ignition  of  the  compressed  charge 
in  the  crank  case,  at  the  time  when  the  piston  uncovers 
the  transfer  port.  The  charge  burned  in  the  crank  case 
is  obviously  useless  as  a  producer  of  power  and  hence  such 


Cylinder  Head 


Water  By -Pass 
to  Cylinder 


TTransfer  Port 

Piston  Ring 

Piston  Pi 

Jjston  Pin  Bushing ___ 
Oil  Gro 


"Upper  Crank  Cas£ 

Connecting  Rod 

Hand  Hole 

Plate 
Crank  Sha 


Lower  Crank  Case 
Connecting  Rod  Cap 


Oil  Scoop 


FIG.  45  (c). — Sectional  Elevation  of  Fairbanks-Morse  Marine  Engine. 


combustion  means  a  missed  cycle,  if  nothing  more.  Back 
firing  is  due  to  the  ignition  of  the  mixture  entering  the  cylinder, 
ignition  being  produced  by  the  hot  gases  of  the  previous 
charge  or  by  glowing  carbon  on  the  face  of  the  piston. 
When  the  incoming  stream  is  thus  ignited,  the  flame  strikes 
back,  traveling  down  the  transfer  passage  and  into  the 
crank  case  causing  a  "  crank  case  explosion." 

To   prevent   such   action,    the  transfer  passage  in  this 
engine  contains  a  piece  of  wire  screen  pleated  in  such  a  way 


XII.     TYPES  OF  GAS  AND  GASOLINE  ENGINES     129 

as  to  presents  large  surface  to  the  gas  in  the  passage.  This 
screen  acts  in  the  same  way  as  that  surrounding  a  miner's 
safety  lamp,  that  is,  it  serves  as  a  quick  absorber  of  heat  in 
case  of  a  strike-back,  thus  reducing  the  temperature  of  the 
burning  gases  to  so  low  a  value  that  the  flame  is  extinguished 
and  does  not  reach  the  mixture  still  left  in  the  crank  case. 

Cooling  of  the  engine  is  effected  by  drawing  water  from 
outside  of  the  boat  and  forcing  it  through  the  jackets. 
This  pumping  is  done  by  means  of  the  small  plunger  pump 
P,  Fig.  45  (a),  which  is  operated  by  an  eccentric  E  on  the 
crank  shaft.  The  pump  discharges  into  the  lower  part  of 
the  cylinder  jacket  through  the  pipe  A,  the  water  flowing 
up  through  the  jacket,  then  through  the  by-pass  into 
the  head  as  shown  in  Fig.  45  (c),  and  from  the  head  to  the 
jacket  around  the  exhaust  pipe. 

Ignition  is  by  a  make-and-break  igniter  located  in 
the  side  of  the  clearance  space  as  shown  in  Fig.  45  (6). 
The  movable  electrode  is  operated  by  an  extension  of  the 
pump  plunger  as  shown.  The  time  of  ignition  is  con- 
trolled by  means  of  a  hand  lever  indicated  by  C  in  Fig.  45  (6) . 

The  main  bearings  are  lubricated  by  compression  grease 
cups,  while  the  moving  parts  within  the  engine  are  lubricated 
by  oil  fed  from  the  cup  shown  in  Fig.  45  (a).  One  of  the' 
leads  from  this  cup  enters  the  cylinder  wall  and  supplies 
oil  to  the  piston  and  the  hollow  piston  pin.  From  the 
latter,  the  oil  flows  to  the  exterior  of  the  pin  through  a 
hole  drilled  at  right  angles  to  the  bore. 

The  other  lead  from  the  cup  enters  the  wall  of  the 
crank  case  and  is  arranged  to  drop  oil  into  the  interior  of 
a  centrifugal  or  ring  oiler,  not  shown  in  the  figures.  This 
ring  is  fastened  to  the  crank  cheek  with  its  centre  in  line 
with  that  of  the  crank  shaft.  A  groove  is  turned  on  its 
inner  circumference  so  that  when  in  rotation  any  oil  which 
gets  into  this  groove  will  be  pressed  against  the  surface 
of  the  groove  with  a  definite  pressure  due  to  the  centrifugal 
action.  This  oil  passes  through  a  hole  in  the  ring  into  a 


130 


GAS  POWEIl 


, 


XII.     TYPES  OF  GAS  AND   GASOLINE  ENGINES     131 

hole  along  the  centre  line  of  the  crank  pin  and  then  through 
a  hole  at  right  angles  to  the  surface  of  the  pin. 

66.  The  Foos  Single-cylinder  Horizontal  Engine.  This 
engine,  constructed  by  the  company  of  the  same  name, 
is  built  substantially  as  shown  in  Figs.  46  (a),  (6),  (c)  and 
(d),  in  sizes  from  3  to  90  h.p.  to  operate  on  the  ordinary 


FIG.  46  (6). — The  Foos  Gas  Engine,  Half-time  Mechanism. 

gas  and  liquid  fuels.  It  operates  on  the  four-stroke  Otto 
cycle  and  is  governed  either  by  hit-and-miss  or  by  throttling 
methods,  depending  upon  the  purpose  for  which  power  is 
supplied. 

The  inlet  and  exhaust  valves  are  operated  positively  by 
the  cams  V  and  U,  Fig.  46  (6),  respectively.  *  These  cams 
push  on  rollers  as  shown  in  Fig.  46  (6),  and  the  motiosn 


132 


GAS   POWER 


given  to  these  rollers  are  transmitted  through  cranks  and 
rods  within  the  frame  of  the  engine  until  finally  imparted 
to  the  valves  by  the  bell  cranks  shown  in  Figs.  46  (a)  and 
(c).  The  cams  are  fastened  to  the  shaft  of  the  large  spur 
gear  G,  Fig.  46  (b),  which  meshes  with  the  pinion  on  the 
crank  shaft  as  shown.  The  ratio  of  diameters  for  these 


Priming  Cock 


FIG,  46  (c), — The  Foos  Gas  Engine,  Section  Showing  the  Valves. 

gears  is  two  to  one,  giving  the  half  speed  required  at  the 
cams  for  four-stroke  operation. 

Hit-and-miss  governing  is  effected  by  cutting  out  fuel 
only  and  allowing  the  inlet  and  exhaust  valves  to  function 
as  usual.  The  rod  J,  shown  in  Fig.  46  (d),  causes  the 
admission  of  fuel  when  it  is  pushed  toward  the  cylinder 


XII.     TYPES  OF  GAS  AND  GASOLINE  ENGINES     133 

by  the  plate  F  on  the  arm  C,  which  in  turn  is  operated  by  a 
cam  on  the  engine  side  of  the  half-time  gear  G.  The  plate 
F  imparts  motion  to  the  rod  J  through  the  hinged  block 
B,  which,  whenever  a  miss  is  to  occur,  is  forced  toward  the 
engine  and  out  of  the  path  of  F  by  means  of  the  finger  A, 
operated  by  the  governor.  Excessive  speed  causes  the 


FIG.  46  (d). — Foos  Gas  Engine,  Governing  Mechanism. 

weights  of  the  governor  G  to  move  out,  drawing  the  spindle 
of  the  governor  toward  the  gears  and  pressing  on  a  roller 
D  at  the  upper  end  of  finger  A.  The  speed  of  the  engine 
can  be  regulated  while  in  operation  by  turning  the  milled 
wheel  H ,  which  changes  the  position  of  the  pin  on  which  A 
swings. 


134  GAS  POWER 

The  ignition  apparatus  is  of  the  wipe  jump-spark  type 
and  was  described  and  illustrated  in  Chapter  VIII. 

67.  The  Bessemer  Gas  Engine.  One  form  of  this 
engine,  which  is  manufactured  by  the  Bessemer  Gas  Engine 
Company,  is  shown  in  Figs.  47  (a)  and  (6).  The  former 
is  an  elevation  of  the  operating  side,  the  latter  a  longitudinal 
section  on  the  centre  line  of  the  engine.  It  is  a  single-acting 
engine,  operating  on  the  two-stroke  principle,  is  built  with  a 
crosshead,  and,  in  the  form  shown,  has  an  enclosed  crank  case. 

The  open  side  of  the  piston  is  used  for  the  precompres- 
sion  so  that,  while  the  head  end  of  the  cylinder  is  the  work- 
ing end  as  usual,  the  crank  end  is  really  a  charging  pump. 

During  the  instroke  of  the  piston— toward  the  left  in 
Fig.  47  (6)— air  flows  into  the  charging  pump  through  the 
air  pipe  A  and  the  automatic  admission  valve  V.  The 
seat  of  this  valve  is  drilled  as  shown,  the  holes  connecting 
with  the  gas  pipe  indicated  by  G  in  Fig.  47  (a).  The 
valve  therefore  serves  as  a  mixing  valve,  admitting  gas  to 
the  air  flowing  through  it  so  that,  at  the  end  of  the  instroke 
of  the  piston,  the  charging  pump  is  filled  with  a  combustible 
mixture.  This  mixture  is  compressed  during  the  outstroke 
until  the  piston  uncovers  the  inlet  port  /  Fig.  47  (6),  at 
which  time  the  new  charge  begins  to  flow  from  the  pump  to 
the  engine  cylinder  through  the  passage  P,  and  to  more  or 
less  perfectly  replace  the  burned  gases  of  the  previous 
stroke,  which  flow  out  through  the  exhaust  port  E. 

The  piston  compresses  this  new  charge  into  the  combus- 
tion chamber  on  the  next  instroke  and  ignition  and  expan- 
sion follow  in  the  usual  way,  the  next  cylinder  charge  being 
drawn  into  and  compressed  in  the  charging  pump,  while 
the  charge  we  have  been  following  is  being  compressed 
and  expanded  in  the  engine  cylinder. 

Ignition  is  effected  by  a  make-and-break  igniter  placed 
in  the  center  of  the  head  of  the  cylinder  and  operated  from 
the  crank  shaft  by  means  of  the  push  rod  indicated  by 
R  in  Fig.  47  (a). 


XII.     TYPES  OF  GAS  AND  GASOLINE  ENGINES     135 


-§ 


136 


GAS  POWER 


XII.     TYPES  OF  GAS   AND  GASOLINE  ENGINES     137 

The  engine  is  governed  by  the  quality  method,  the 
supply  of  gas  to  the  admission  valve,  T',  Fig.  47  (6),  being 
controlled  by  the  throttle  valve,  T7,  Fig.  47  (a),  which  is 
operated  by  linkage  from  the  flyball  governor  F  as  shown. 
The  governor  is  driven  from  the  crank  shaft  by  means  of 
gearing. 

68.  Engine  Manufactured  by  American  Car  Wheel  Co. 
A  representative  example  of  single-acting,  tandem  engines 
is  shown  in  Fig.  48  (a),  which  gives  a  side  elevation  of 
one  of  several  types  manufactured  by  the  above  named 
company.  This  particular  model  is  listed  in  sizes  between 
30  and  120  h.p  ,  but  the  company  builds  other  models  in 
larger  sizes.  All  operate  on  the  four-stroke  principle. 

The  longitudinal  section  of  the  engine  of  Fig.  48  (a)  is 
shown  in  Fig.  48  (6),  and  a  cross-section  through  the  valves 
of  one  cylinder  is  given  in  Fig.  48  (c). 

As  shown  in  Figs.  48  (a)  and  48  (6),  the  engine  is  built 
with  a  crosshead  and  with  enclosed  guides  and  crank  case. 
The  closed  construction  greatly  simplifies  the  lubrication, 
at  the  same  time  giving  a  more  cleanly  engine  and  engine 
room. 

It  will  l)e  observed  that  the  part  of  the  piston  rod  which 
connects  the  two  pistons  must  pass  through  the  cylinder 
head  of  the  forward  cylinder.  This  necessitates  some  form 
of  packing  to  prevent  leakage  of  high-pressure  gas  from  this 
cylinder.  The  long  water-cooled  sleeve  which  surrounds 
the  rod  is  bored  to  give  small  clearance  and  serves  to  cool 
any  gas  leaking  along  the  rod,  and  thus  reduce  the  pressure. 
Further  leakage  of  this  cooled  gas  is  then  practically  entirely 
eliminated  by  cast-iron  rings  in  a  stuffing-box  fitted  to  the 
outside  of  the  head  as  shown. 

Starting  is  effected  by  compressed  air  operating  on 
the  rear  piston  and  admitted  through  the  valve  shown 
in  the  rear  cylinder  head. 

The  cam  shaft  or  half-time  shaft  is  driven  by  spiral 
gears  from  the  crank  shaft,  and  the  inlet  and  exhaust 


138 


GAS  POWER 


XII.     TYPES  OF  GAS  AND  GASOLINE  ENGINES     139 


140 


GAS   POWER 


valves  are  both  operated  by  one  cam  on  this  shaft  as  shown 
in  Figs.  48  (c)  and  48  (d).  As  in  most  of  the  larger  engines, 
the  inlet  valve  is  above  and  the  exhaust  valve  beneath, 
and  both  operate  vertically. 

Governing  is  effected  by  throttling  the  mixture  by  means 
of  the  governor  valve  shown  in  Fig.  48   (c).     This  valve 


Speed  Adjustment 
Igniter 


FIG.  48  (c'). — Section  through  Valves,  American  Car  Wheel  Co.  Engine. 

is  merely  a  circular  grid  which  is  raised  and  lowered  by  the 
governor  in  such  a  way  as  to  make  its  ports  register  more 
or  less  perfectly  with  the  stationary  ports  surrounding  it 
and  leading  into  the  mixture  pipe  and  thence  to  the  inlet 
valve  and  cylinder.  For  maximum  load,  the  ports  register 
perfectly;  for  friction  load,  the  valve  shifts  until  the  sta- 
tionary ports  are  almost  blocked  by  the  grids. 


XII.     TYPES  OF  GAS  AND  GASOLINE  ENGINES     141 

The  air  and  gas  are  admitted  to  the  inside  of  the  governor 
valve  as  shown  and  mix  during  their  passage  from  that 
point  to  the  inlet-valve  of  the  engine.  The  cock  shown  in 


! 

FIG.  48  (d). — Valve  Gear  for  the  Larger  Type  of  Engines. 

the  gas  pipe  is  used  for  hand  control  of  the  proportion  of 
gas  in  the  mixture. 

The  valve  gear  used  on  the  larger  engines  is  slightly  dif- 
ferent and  is  shown  in  Fig.  48 '  (d).     The  inlet  and  exhaust 


142  GAS   POWER 

valves  are  operated  by  one  cam  as  before,  but  the  stroke 
of  the  inlet  valve  is  made  variable  and  put  under  governor 
control.  This  is  effected  by  using  a  movable  block,  a 
in  Fig.  48  (d),  for  the  fulcrum  of  the  upper  link  of  the 
inlet  mechanism  and  connecting  the  governor  so  as  to  slide 
this  block  toward  and  from  the  inlet  valve  stem  as  required 
to  decrease  or  increase  the  amount  of  opening  of  that 
valve. 

Carried  on  the  stem  of  the  inlet  valve  and  moving  with 
it,  is  a  circular  grid  with  two  ports,  the  lower  forxair  and  the 
upper  for  gas.  These  ports  are  so  arranged  that,  as  the 
valve  opens,  air  is  first  admitted  and  blows  away  from  the 
inlet  valve  any  hot  or  burning  gas  which  may  remain  over 
from  the  last  cycle,  thus  preventing  ignition  of  the  new 
charge.  The  gas  port  opens  with  further  motion  of  the 
valve  and  a  mixture  is  then  formed  by  the  air  and  gas  as 
they  pass  the  inlet  valve.  The  relative  proportions  of  the 
mixture  are  set  by  hand  by  means  of  the  butterfly  throttle 
shown  in  the  gas  pipe. 

Governing  on  the  larger  engines  is  effected  by  a  combina- 
tion of  quantity  and  quality  methods  as  a  result  of  the 
variable  stroke  of  the  inlet  valve  and  the  arrangement  of 
ports  in  the  grid  above  it.  For  the  higher  loads,  the  quality 
of  the  mixture  remains  practically  constant  and  is  simply 
throttled  in  proportion  to  the  load  by  the  ports  and  inlet 
valve.  For  the  lower  loads,  however,  when  the  motion 
of  the  valves  is  small,  the  air  port  is  relatively  wider  open 
than  the  gas  port  and  there  is  a  certain  amount  of  quality 
governing  superimposed  on  the  quantity  governing,  thus 
decreasing  the  lower  loop  loss. 

The  exhaust  valve  in  these  larger  engines  is  made  hollow 
and  -fitted  with  a  hollow  stem  as  shown  in  the  figure  so  that 
it  can  be  water  cooled. 

69.  The  Bruce-Macbeth  Gas  Engine.  This  engine  is 
made  in  two-  and  four-cylinder  vertical  units.  A  view  and 
part  section  of  a  large,  four-cylinder  engine  is  shown  in  Fig. 


XII.     TYPES  OF  GAS  AND   GASOLINE  ENGINES     143 

49  (a),  and  a  vertical  cross-section  through  one  cylinder  is 
given  in  Fig.  49  (6). 

The  engine  operates    on    the    four-stroke,   Otto   cycle, 
but  the  multiplicity  of  cylinders  gives  a  well-distributed  set 


of  impulses,  so  that  comparatively  small  flywheels  can  be 
used. 

The  inlet  and  exhaust  valves,  I  and  E  in  Fig.  49  (a),  are 
placed  in  the  cylinder  head  with  their  stems  vertical  and  are 


144  GAS  POWER 

carried  in  cages  so  that  valve,  spring,  and  cage  are  easily 
removed  as  a  unit  for  inspection  or  grinding.  The  valves 
are  operated  by  short  rocker  arms  from  an  overhead  cam 
shaft  as  indicated  in  Fig.  49  (6).  This  shaft  is  driven 
at  half  the  speed  of  the  crank  shaft  by  means  of  bevel  and 
spur  gears  and  intermediate  horizontal  and  vertical  shafts 
as  shown  in  the  same  figure.  The  vertical  shaft  carries 
the  governor,  the  operation  of  which  will  be  described  later. 

As  in  most  vertical  engines  designed  in  this  country, 
this  engine  is  built  with  an  enclosed  crank  case  fitted  with 
large  removable  plates  which  give  ready  access  to  the  interior. 
The  lower  part  of  this  case  is  filled  with  oil  to  such  a  level 
that  the  lower  ends  of  the  connecting  rods  strike  the  oil 
when  near  their  lowest  positions  and  thus  splash  it  around 
within  the  case  and  over  the  various  parts  which  require 
lubrication.  This  is  known  as  the  splash  system  of  lubrica- 
tion and  is  very  commonly  usei  with  this  type  of  engine, 
although  there  is  now  a  tendency  to  adopt  pressure  feed  to 
the  principal  rubbing  surfaces  in  large  engines  so  as  to 
make  lubrication  more  certain  and  less  a  matter  of  chance. 

Governing  is  by  throttling,  the  governor  collar  operating 
the  double  throttle  valve  by  means  of  the  lever  L,  which 
is  pivoted  at  the  centre  line  of  the  engine  as  shown  in 
Fig.  49  (6).  Outward  movement  of  the  governor  weights 
with  increasing  speed  results  in  moving  the  governor  end 
of  the  lever  L  downward,  thus  moving  the  throttling  valve 
upward.  It  will  be  observed  that  the  gas  and  air  are 
throttled  separately  and  that  they  flow  through  separate 
passages  after  passing  the  throttle  valve.  They  remain 
separated  in  this  way  until  they  reach  the  inlet  valve, 
/  in  Fig.  49  (a),  the  mixture  being  formed  as  they  pass  that 
valve.  There  is,  therefore,  no  mixture  stored  outside  of 
the  cylinder  and  backfires  cannot  occur. 

The  proportion  of  gas  to  air  is  set  by  hand  by  means 
of  the  indicating  gas  and  air  valves  V  and  V  shown  in 
Fig.  49  (6). 


XII.     TYPES   OF  GAS  AND  GASOLINE   ENGINES     145 


Gas  Arr 


FIG.  49  (b). — Section  of  the  Bruce-Macbeth  Gas  Engine. 


146  GAS  POWER 

Ignition  is  by  means  of  a  high-tension  jump  spark,  the 
spark  plug  or  plugs,  P  in  Fig.  49  (6),  being  located  at  the 
side  of  the  combustion  space. 

Starting  is  effected  by  the  use  of  compressed  air,  which 
is  admitted  through  the  valve  lettered  A  in  Fig.  49  (6). 

70.  The  Buckeye  Gas  Engine.  The  Buckeye  Engine 
Company  manufactures  both  single-acting  and  double-acting 
tandems,  but  only  the  latter  type  will  be  described.  A 
view  of  this  engine  is  shown  in  Fig.  50  (a),  and  a  .longitudinal 
section  is  shown  in  Fig.  50  (6). 

(6)  There  are,  as  in  all  engines  of  this  type,  five  prin- 
cipal stationary  parts,  namely,  the  main  frame  or  bed, 
the  cylinder  connected  therewith  or  the  bed  end  cylinder, 
'the  intermediate  or  distance  piece,  the  far  or  out  end 
cylinder,  and  the  tail  piece.  The  bed  is  rigidly  bolted 
to  the  foundation,  but  the  distance  and  tail  pieces  are 
free  to  slide  back  and  forth  in  the  direction  of  the  length 
of  the  engine,  thus  permitting  changes  of  length  with 
varying  temperature. 

The  cylinders  are  cast  with  a  split  jacket,  that  is,  part 
of  the  jacket  wall  is  omitted  at  the  centre  of  length  of  the 
cylinder  as  shown  in  Fig.  50  (b).  This  opening  is  later  closed 
by  means  of  a  band  drawn  tight  by  bolts  as  shown  in  Figs. 
50  (a)  and  50  (6).  This  construction,  which  is  now  used 
on  nearly  all  large  gas-engine  cylinders,  simplifies  the  cast- 
ing, prevents  excessive  casting  strains,  and  prevents  tem- 
perature stresses  resulting  from  the  differential  expansion 
of  the  jacket  and  working  bore. 

The  cylinder  ends  are  closed  with  water-cooled  heads  as 
shown  in  Fig.  50  (6).  Metallic  packing  outside  of  these 
heads  prevents  the  leakage  of  gas  around  the  rod. 

The  water-cooled  pistons  are  clamped  against  shoulders 
on  the  water-cooled  rods  by  large  flush  nuts  as  shown  in 
Fig.  50  (6).  The  cooling  water  enters  the  system  through 
a  sliding  connection  at  the  intermediate  crosshead  and 
flows  in  both  directions  through  the  rods  and  pistons  until 


XII.     TYPES  OF  GAS  AND  GASOLINE  ENGINES     147 


148  GAS   POWER 

it  is  finally  discharged  into  chambers  in  the  frame  from 
pipes  carried  by  the  main  and  tail  crossheads.  Such  a  pipe 
is  shown  in  Fig.  50  (6)  hanging  down  from  the  tail  cross- 
head. 

The  inlet  valves,  as  usual  in  this  type,  are  placed  at  the 
tops  of  the  cylinders  and  the  exhaust  valves  are  located 
below.  The  arrangement  is  well  shown  in  Figs.  50  (6) 
and  50  (c),  the  latter  being  a  cross-section  through  a 
combustion  chamber.  The  exhaust-valve  cage  is  very 
carefully  water  cooled  and  in  large  sizes  the  exhaust 
valves  are  similarly  protected.  Both  sets  of  valves 
are  operated  from  a  half-time  shaft  by  means  of  eccen- 
trics and  rocking  levers  as  shown  to  best  advantage 
in  Fig.  50  (c). 

The  governing  mechanism  used  on  these  engines  is  par- 
ticularly interesting.  It  produces  a  combination  of  quality 
and  quantity  governing  so  arranged  that  at  the  higher 
loads  (above  J  or  f,  depending  on  gas  used)  the  governing 
is  almost  entirely  effected  by  decreasing  the  amount  of 
gas  in  the  charge,  thus  maintaining  a  high  compression 
pressure.  For  lower  loads,  the  proportions  of  gas  and  air 
remain  more  nearly  constant,  the  governing  being  done 
almost  entirely  by  throttling.  Thus  the  mixture  is  never 
made  so  lean  that  abnormally  slow  burning  results,  and  the 
efficiency  is  well  sustained  over  a  large  range. 

Governing  is  effected  by  means  of  the  double-seated 
throttle  valve  T  and  the  gas  valve  V.  The  throttle 
valve  T  is  always  open,  but  the  degree  of  opening  is 
varied  by  the  governor  which  moves  the  lever  L,  and, 
with  it,  the  lever  L'  about  the  pin  in  the  upper  end  of 
the  small  bracket.  The  governor  connection  is  not  shown 
in  the  figure. 

The  gas  valve  V  is  always  closed  when  the  main  inlet 
valve  is  closed,  being  held  to  its  seat  by  the  spring  S.  It  is 
opened  when  necessary  by  the  collar  C  on  the  gas-valve 
stem,  which  is  drawn  up  by  the  arched  lever  A  which  ful- 


XII.     TYPES  OF  GAS  AND  GASOLINE  ENGINES     149 


r" 
'ot 


PQ 


f 


§ 

c5 

s 


150  GAS  POWER 

crums  on  the  end  of  the  lever  L  and  is  moved  when  the 
inlet-valve  operating  lever  0  depresses  that  valve  by  rota- 
ting clockwise  about  the  pin  at  its  left  hand  end.  When  the 
engine  is  Carrying  the  maximum  load,  the  valves  T  and  V 
so  proportion  the  mixture  as  to  give  maximum  efficiency. 
As  the  load  falls  off  the  lever  L  is  moved  clockwise  by  the 
governor  so  that  the  opening  of  the  throttle  valve  T  and  the 
lift  of  the  gas  valve  V  are  both, -decreased.  At  full  load, 
the  opening  of  the  throttle  valv'e  T  is  so  great  that  the  de- 
creased opening  occurring  with  falling  load  has  little  throt- 
tling effect  until  the  load  has  fallen  to  between  J  and  J  of 
maximum,  the  exact  value  varying  with  the  gas  used.  It 
thus  results  that,  for  the  higher  loads,  there  is  practically 
no  throttling  so  far  as  the  total  charge  is  concerned,  but  that 
the  quantity  of  gas  in  that'  charge  is  decreased. 

For  further  decrease  in  load,  the  throttling  effect  of  the 
valve  T  becomes  more  important  while  the  variation  in 
the  lift  of  the  valve  V  becomes  less  important,  so  that  the 
quality  of  the  mixture  remains  more  nearly  constant  and 
governing  is  due  almost  entirety  to  throttling  of  the 
mixture. 

The  collar  C  on  the  gas-valve  stem  is  placed  in  such  a 
position  that  the  stem  may  rise  a  certain  distance  at  all 
loads  before  the  gas  valve  is  open.  As  a  result,  when  the 
inlet  valve  first  opens,  air  only  passes  the  throttle  T  and  enters 
the  cylinder,  thus  blowing  away  any  hot  or  burning  gases 
remaining  over  from  the  previous  stroke.  Similarly,  the 
gas  valve  closes  before  the  inlet  valve  is  entirely  closed  so 
that  the  mixing  chamber  outside  of  the  throttle  valve  and 
the  passage  outside  of  the  inlet  valve  are  left  full  of  air  and 
not  of  mixture.  It  is  thus  impossible  to  get  a  backfire 
when  the  inlet  valve  is  next  opened. 

Ignition  is  effected  by  the  electrically  operated  igniters 
E,  Figs.  50  (a)  and  (c).  Two  are  used  so  as  to  increase 
reliability  and  also  to  increase  the  rapidity  of  combustion 
with  slow-burning  mixtures. 


XII.     TYPES  OF  GAS  AND  GASOLINE  ENGINES     151 


152  GAS  POWER 

Lubrication  in  the  engine  shown  is  by  forced  feed.  The 
pistons  and  cylinders  are  supplied  with  lubricating  oil  by 
means  of  a  pump  driven  from  the  end  of  the  half-time 
shaft  as  shown  in  Fig.  50  (a),  while  the  crossheads  and 
main  bearings  are  supplied  with  oil  under  gravity  head  as 
shown  in  the  same  figure. 


CHAPTER    XIII 
MODERN    TYPES    OF    OIL    ENGINES 

71.  The  Peterson  Kerosene  Engine.  This  engine  is 
made  by  a  number  of  firms  operating  under  the  patents 
granted  to  John  and  F.  E.  Peterson.  It  is  very  simple  and 
represents  a  satisfactory  commercial  solution  of  the  kerosene 
problem  in  the  case  of  small  engines,  this  type  being  built 
only  up  to  10  h. p. 

In  Fig.  51  (a)  is  shown  a  view  of  the  engine  and  cooling- 
water  tank  mounted  on  skids,  a  very  convenient  arrange- 
ment for  agriculturists  and  similar  users  of  small  power.  A 
section  of  the  engine  with  the  fuel-feeding  device  slightly 
distorted  is  given  in  Fig.  51  (6).  Fig.  51  (c)  shows  details 
of  the  fuel-feeding  device  to  a  larger  scale. 

The  engine  operates  on  the  two-stroke  principle,  using 
the  crank  case  and  open  end  of  the  piston  for  a  charging 
pump.  On  the  upstroke  of  the  piston,  air  is  drawn  into 
the  crank  case  through  the  air  valve  A  in  Fig.  51.  (6).  On 
the  return  stroke,  the  air  thus  trapped  in  the  crank  case  is 
compressed  by  the  descending  piston  until  the  latter  uncovers 
the  inlet  port  /  in  the  cylinder  wall.  When  this  occurs, 
the  air  rushes  through  the  by-pass  B,  strikes  the  deflecting 
plate  D  on  the  piston,  turns  upward  and,  in  the  ideal  case, 
completely  displaces  the  burned  gases  of  the  previous 
cycle  by  driving  them  out  through  the  exhaust  port  E,  which 
was  uncovered  by  the  piston  just  before  it  uncovered  the 
inlet  port  7. 

While  the  air  is  entering  the  cylinder  a  charge  of  fuel 
is  sprayed  into  it  from  the  nozzle  AT  in  a  way  which  will 

153 


154  GAS  POWER 

be  explained  later.  Thus,  when  the  piston  starts  on  the 
upstroke,  there  is  a  charge  of  combustible  mixture  above  it, 
and  as  soon  as  the  ports  have  been  covered,  compression 
begins.  Ignition  is  effected  near  the  end  of  the  compres- 
sion stroke  by  means  of  the  jump-spark  plug  shown  in  the 


FIG.  51  (a). — Peterson  Kerosene  Engine. 

head  of  the  cylinder  and  the  expansion  follows  as  the  pis- 
ton again  moves  out. 

,The  fuel-feeding  device,  shown  in  detail  in  Fig.  51  (c), 
operates  in  the  following  manner:  the  float  F  controls  the 
fuel  level  by  means  of  the  ball  carried  at  the  lower  end  of 


XIII.     MODERN  TYPES   OF  OIL  ENGINES          155 


FIG.  51  (6). — Section  of  Peterson  Kerosene  Engine. 


156 


GAS  POWER 


its  stem,  shutting  off  the  fuel  supply  pipe  whenever  the 
proper  level  is  attained.  The  lower  ball,  which  is  perfectly 
free,  acts  simply  as  a  check  valve  to  prevent  the  fuel  in  the 
chamber  C  from  flowing  back  to  the  storage  reservoir. 

This  reservoir  is  located  below  the  level  of  the  chamber 
C  and  the  fuel  flows  into  C  during  the  upstroke  of  the  piston 


FK;.  51  (r).- — Fuel  Feeding  Apparatus  for  the  Peterson  Engine. 


because  of  the  pipe  P,  which  connects  C  with  the  crank 
case,  thus  insuring  a  low  pressure  in  C  when  there  is  a  low 
pressure  beneath  the  piston. 

When  the  piston  moves  down  and  compresses  the  air 
in  the  crank  case,  this  higher  pressure  acts  on  the  fuel 
surface  in  C,  so  that,  when  the  nozzle  within  the  inlet  port 


XIII.     MODERN  TYPES  OF  OIL  ENGINES          157 

of  the  engine  is  uncovered  by  the  piston,  fuel  is  sprayed  or 
atomized  into  the  cylinder.  As  the  new  charge  of  air  is 
also  passing  into  the  cylinder  at  that  instant,  the  fuel 
spray  is  picked  up  by  this  air  to  form  a  combustible  mixture. 
This  action  is  assisted  by  the  hot  deflector  plate  D  against 
which  air  and  fuel  strike  as  they  enter  the  cylinder. 

Governing  is  effected  by  throttling  at  the  air  inlet  valve 
A,  the  lift  of  this  valve  being  controlled  by  the  governor. 
For  light  loads,  only  a  small  quantity  of  air  enters  the  crank 
case  and  it  follows  that  the  highest  pressure  attained  in 
the  crank  case  will  be  correspondingly  low.  This  will 
result,  however,  in  spraying  less  fuel  during  admission 
and  the  quantity  of  fuel  will,  roughly,  follow  the  quantity 
of  air. 

While  this  engine  is  primarily  intended  to  utilize  kerosene, 
it  will  work  equally  well  on  gasoline  or  other  volatile  fuel. 

72.  The  Hornsby-Akroyd  Oil  Engine.  This  engine, 
which  is  of  English  origin  and  was  one  of  the  first  to  suc- 
cessfully utilize  kerosene,  has  been  made  in  this  country 
by  the  De  La  Vergne  Machine  Company  for  a  number  of 
years.  During  this  time  it  has  been  considerably  improved 
in  detail,  so  that  it  is  now  capable  of  handling  most  of  the 
heavier  petroleum  fuels.  It  is  used  with  oils  testing  down 
to  about  25°  Be.  It  is  built  in  single-cylinder  units  up  to 
85  brake  horse-power,  and  in  double  or  twin  units  up  to 
100  h.p. 

An  external  view  of  the  single-cylinder  engine  is  given 
in  Fig.  52  (a),  a  longitudinal  section  in  Fig.  52  (6)  and  a 
cross-section  through  the  valve  box  in  Fig.  52  (c) . 

This  engine  operates  on  a  four-stroke  cycle  practically 
identical  with  that  of  Otto  so  far  as  the  valve  and  pis- 
ton events  are  concerned.  The  inlet  and  exhaust  valves 
are  carried  in  a  box  fastened  to  one  side  of  the  cylinder 
as  shown  in  Fig.  52  (c).  the  gases  entering  and  leaving  the 
cylinder  through  the  valve  port  shown  in  Fig.  52  (6).  The 
valves  function  like  those  of  any  four-stroke  Otto  engine 


158 


GAS  POWER 


XIII.     MODERN  TYPES  OF  OIL  ENGINES 


with  the  exception  that  the  inlet  valve  admits  air  only 
during  the  suction  stroke. 

Fastened  to  the  head  end  of  the  cylinder  is  a  vessel 
called  the  vaporizer,  which  communicates  with  the  interior 
of  the  cylinder  through  a  comparatively  narrow  port  or  neck 
as  shown  in  Fig.  52  (6).  This  vaporizer  is  heated  to  a  dull 
red  by  means  of  a  blow  torch  before  starting  the  engine, 


Vaporizer- 


FIG.  52  (6).— Longitudinal  Section,  De  La  Vergne  Oil  Engine. 

after  which  the  combustion  which  occurs  within  it  liberates 
sufficient  heat  to  keep  it  at  the  proper  temperature. 

While  air  is  being  drawn  into  the  cylinder  during  the 
suction  stroke  the  plunger  oil  pump,  which  is  operated 
from  the  inlet  valve  lever  as  shown  in  Fig.  52  (c),  forces 
a  charge  of  oil  through  a  spray  nozzle  into  the  heated 
vaporizer.  The  oil  is  vaporized  by  the  hot  walls,  but 
cannot  burn  as  there  is  practically  no  oxygen  within  the 


160 


GAS  POWER 


vaporizer.  During  the  compression  stroke,  some  of  the 
cylinder  charge  of  air  is  forced  into  the  vaporizer,  and 
toward  the  end  of  that  stroke  the  mixture  thus  formed 
reaches  combustible  proportions  and  is  ignited  by  the  hot 
v.alls,  causing  a  rapid  rise  of  pressure  similar  to  that  of  the 
Otto  cycle.  The  hot  gases  then  expand  and  are  finally 
discharged  through  the  exhaust  valve.  It  should  be  ob- 


FIG.  52  (r). — Cross-section,  De  La  Vergne  Oil  Engine. 


served  that  the  vaporizer  remains  filled  with  hot  burned 
gases  at  the  end  of  the  exhaust  stroke,  thus  preventing  too 
early  ignition  of  the  next  charge  of  oil. 

Governing  is  very  simply  effected  by  making  the  oil 
pump  discharge  more  oil  than  can  be  used  even  at  full 
load,  and  by-passing  the  excess  back  to  the  oil  reservoir 
by  a  valve  under  governor  control  as  shown  in  Fig.  52  (a). 


XIII.     MODERN  TYPES  OF  OIL  ENGINES          161 

This  type  of  engine  seldom  gives  a  thermal  efficiency 
on  the  brake  higher  than  about  18  per  cent,  which  is  con- 
siderably lower  than  the  value  attained  by  oil  engines  of 
later  type,  but  it  has  the  advantage  of  being  lighter,  cheaper, 
and  simpler  than  the  more  economical  engines. 

The  vaporizer  gradually  fills  up  with  carbon  formed  by 
the  "  cracking  "  of  the  oil  during  vaporization  and  it  must 
therefore  be  cleaned  out  at  intervals.  With  light  fuels, 
cleaning  need  not  be  of  frequent  occurrence,  but  the 


FIG.  53  (a).— The  Muncie  Oil  Engine. 

periods  between  cleanings  become  very  short  with  some  of 
the  heavier  oils. 

73.  The  Muncie  Oil  Engine.  This  engine  is  built  by 
the  Muncie  Gas  Engine  and  Supply  Company,  and  is  sold 
to  operate  on  all  petroleum  fuels  from  gasoline  to  crude 
oil  inclusive.  Its  greatest  field  of  application  is  in  the  use 
of  kerosene  and  the  distillates. 

A  view  of  the  working  side  of  the  engine  is  given  in 
Fig.  53  (a)  and  a  longitudinal  section  in  Fig.  53  (6). 


162 


GAS   POWER 


XIII.     MODERN  TYPES  OF  OIL  ENGINES          163 

The  Muncie  oil  engine  operates  on  the  two-stroke  prin- 
ciple, the  crank  case  being  used  as  the  charging  pump  and 
handling  air  only.  Air  is  drawn  into  the  crank  case  through 
the  valve  A  during  the  compression  ("  in  ")  stroke  of  the 
piston,  and  is  compressed  during  the  outstroke  in  the  usual 
way". 

When  the  piston  uncovers  the  inlet  port  I,  the  air 
passes  from  the  crank  case  to  the  cylinder  and  more  or  less 
perfectly  replaces  the  burned  gases  of  the  previous  cycle. 
The  return  stroke  of  the  piston  then  compresses  this  air, 
together  with  water,  admitted  from  the  jacket  through 
the  regulating  valve  W,  and  fuel  vapor  formed  by  injecting 
oil  through  the  injection  nozzle  A',  so  that  some  of  it  falls 
onto  the  metal  lip  L. 

Ignition  is  effected  by  the  hot  bulb  B,  into  the  interior 
of  which  the  air  carries  part  of  the  fuel  vapor  during  com- 
pression. This  bulb  is  heated  for  starting  by  means  of  a 
blow  torch  shown  in  Fig.  53  (a).  During  operation  the 
successive  internal  combustions  maintain  the  required 
temperature. 

The  use  of  water  prevents  preignition,  smoky  exhaust, 
and  carbon  deposits  as  already  indicated  in  a  previous 
chapter. 

74.  The  Elyria  Oil  Engine.  This  engine,  made  by  the 
Elyria  Gas  Power  Company,  may  be  described  as  a  semi- 
Diesel  type.  It  operates  on  a  cycle  like  that  of  the  Diesel 
engine,  but  this  cycle  is  modified  in  such  a  way  that  the  max- 
imum pressure  attained  in  the  cylinder  is  lower  than  that 
in  the  case  of  the  common  Diesel  engine.  As  a  result, 
the  engine  can  be  built  lighter  and,  therefore,  cheaper,  and 
the  problem  of  attendance  is  also  simplified. 

A  view  of  the  engine  is  given  in  Fig.  54  (a).  Fig.  54  (6) 
shows  a  longitudinal  section  through  the  working  cylinder, 
and  Fig.  54  (c)  shows  a  similar  section  througfrthe  air  pump. 

The  engine  operates  on  the  two-stroke  principle,  scaveng- 
ing air  being  furnished  by  the  differential  piston  Pr,  which 


164 


GAS   POWER 


XIII.     MODERN  TYPES  OF  OIL  ENGINES          165 

is  rigidly  fastened  to,  and  moves  with,  the  main  piston 
P.  The  differential  piston  carries  the  wrist  pin  and  acts 
as  a  crosshead,  thus  relieving  the  main  piston,  which  must 
be  tight  against  high  gas  pressures.  The  scavenging  air 
is  drawn  into  the  scavenging  pump  through  the  pipe  S 
and  discharged  at  a  pressure  of  about  6  pounds  gauge 
into  the  pipe  R,  which  acts  as  a  receiver.  Admission  and 
discharge  are  controlled  by  the  piston  valve  V,  which  is 
really  an  extension  of  pump  piston  A\  (to  be  described 
later)  and  which  serves  as  a  crosshead  for  this  pump. 

Air  passes  from  the  receiver,  through  the  inlet  port  /, 
when  the  main  piston  P  is  at  the  outer  end  of  its  stroke. 
Part  of  this  air  serves  only  as  a  scavenger,  being  lost  through 
the  exhaust  port  E  with  the  burned  gases;  part,  however, 
remains  and  fills  the  cylinder  when  the  piston  starts  on  the 
return  stroke.  This  air  is  compressed  into  the  clearance 
C  and  attains  a  pressure  of  about  400  pounds  per  square 
inch.  This  is  100  (or  more)  pounds  lower  than  the  pres- 
sure commonly  used  in  Diesel  engines. 

At  the  end  of  the  compression  stroke,  the  fuel  needle 
valve  N  is  raised  and  the  oil  is  atomized  into  the  clearance 
space  by  high-pressure  air  as  in  the  ordinary  Diesel  engine. 
This  fuel  injection  continues  at  full  load  during  the  first 
10  per  cent  of  the  stroke.  The  temperature  attained  by  the 
air  in  the  clearance  space  is  high  enough  to  ignite  even 
heavy  oils,  despite  the  low  compression  pressure,  because 
of  the  uncooled  cylinder  cover  U  and  the  false  piston  head 
H  which  are  used  in  this  engine. 

The  air  used  for  blasting  the  fuel  is  compressed  in  three 
stages.  The  first  stage  occurs  in  the  scavenging  pump; 
the  second  stage  is  effected  by  the  piston  AI,  which  draws 
air  from  the  reservoir  R  through  the  valve  B  and  discharges 
it  through  the  valve  D  to  a  receiver  placed  near  the  engine. 
The  third  stage  is  effected  by  piston  A<z,  which  discharges 
through  the  valve  F  directly  to  the  fuel  valve. 

The  pressure  maintained  in  the  receiver  to  which  the 


166 


GAS   POWER 


XIII.     MODERN  TYPES   OF  OIL  ENGINES 


167 


168  GAS  POWER 

second  stage  discharges  is  about  175  to  200  Ibs.,  and  this 
air  is  used  in  starting  the  engine  as  well  as  for  a  supply 
for  the  third  stage.  The  third  stage  discharges  at  pressures 
between  500  pounds  (for  light  loads  and  light  fuels)  and 
1000  pounds  (for  maximum  loads  and  heavy  fuels). 

The  fuel  oil  pump,  indicated  by  0  in  Fig.  54  (a),  is 
driven  by  a  Rites  Inertia  Governor  through  the  linkage 
shown  in  the  figure,  the  stroke,  and  hence  the  quantity  of 
fuel,  being  varied  to  suit  the  load. 

Unlike  the  pure  Diesel  type,  this  engine  will  not,  in 
general,  pick  up  its  cycle  when  rotated  by  high-pressure  air, 
because  the  low  compression  pressure  does  not  create  a 
sufficiently  high  temperature  to  cause  ready  ignition.  Pro- 
vision is  therefore  made  for  starting  on  gasoline,  when 
necessary,  and  then  changing  to  the  regular  fuel  when  the 
engine  has  attained  a  sufficiently  high  temperature. 

The  makers  claim  that  this  engine  will  operate  sat- 
isfactorily on  any  fuel  oil,  and  their  full-load  guarantee 
corresponds  to  a  thermal  efficiency  on  the  brake  of  about 
20  to  22  per  cent.  This  is  considerably  lower  than  the 
values  which  can  be  attained  by  Diesel  engines,  but  this 
is  partly  or  wholly  counterbalanced  by  lower  first  and 
maintenance  costs. 

75.  The  Diesel  Oil  Engine.  The  Diesel  Oil  Engine 
has  come  into  very  extensive  use  during  the  past  decade. 
It  is  made  by  numerous  firms  in  Europe  and  by  several 
in  this  country.  In  its  various  forms,  it  is  without  question 
the  most  perfect  type  yet  developed  for  the  utilization  of 
the  heavier  petroleum  fuels  and  the  by-product  tars  and 
oils.  Combustion  can  be  made  so  nearly  perfect  that  the 
exhaust  is  absolutely  smokeless  and  odorless  even  with  the 
heaviest  fuels. 

The  thermal  efficiency  on  the  brake  is  also  higher  than 
that  of  other  internal  combustion  engines.  The  engine 
is,  however,  handicapped  by  the  facts  that  very  high  pres- 
sures are  used  and  that  there  is  a  great  multiplicity  of 


XIII.     MODERN  TYPES  OF  OIL  ENGINES          169 

small  parts  upon  the  perfect  functioning  of  which  continued 
operation  of  the  engine  depends.  As  a  result  this  type  of 
engine  must  be  built  both  heavy  and  well,  and  it  requires 
a  very  high  class  of  attendance  to  keep  it  in  successful 
operation.  The  first  cost  and  the  maintenance  costs  are 
thus  higher  than  with  other  internal  combustion  engines 
and,  with  the  cheap  fuels  still  obtainable  in  this  country, 
this  fact  has  operated  against  the  extensive  use  of  Diesel 
engines.  Conditions  are  different  in  Europe  and  there  this 
engine  has  been  very  widely  adopted. 

The  construction  adopted  by  the  Busch-Sulzer  Diesel 
Engine  Company  of  St.  Louis  is  shown  in  Figs.  55  (a)  and 
55  (6).  The  first  of  these  is  an  elevation,  part  view  and  part 
section,  of  the  front  or  operating  side  of  a  three-cylinder 
engine,  The  second  shows  a  vertical  section  through  the 
center  line  of  the  first  cylinder,  the  section  being  slightly 
shifted  at  the  top  so  as  to  pass  through  the  centre  line  of  the 
valves  in  order  to  show  them  to  better  advantage. 

This  particular  type  of  Diesel  engine  operates  upon  a 
four-stroke  cycle,  but  there  are  a  large  number  of  Diesel 
engines  built  by  other  manufacturers  which  complete  a 
cycle  in  two  strokes. 

The  valves  are  operated  from  a  half-time  cam  shaft 
located  within  the  crank  case  as  shown  in  Fig.  55  (6).  This 
shaft  is  driven  from  the  crank  shaft  by  spur  gearing,  the 
driving  pinion  being  located  under  the  first  cylinder  as 
shown  in  Fig.  55  (a),  and  the  cam  shaft  gear  being  driven 
through  an  intermediate  gear  as  shown  in  Fig.  55  (6). 

The  admission,  exhaust,  and  fuel  valves  are  located 
in  a  lateral  extension  of  the  cylinder  head  as  shown  in  Fig. 
55  (6).  This  construction  is  quite  different  from  that 
extensively  used  in  Europe,  where  all  valves  in  engines  of 
this  type  are  placed,  plate  down,  in  the  cylinder  head, 
the  fuel  valve  at  the  centre  with  the  admission  valve  on 
one  side  of  it  and  the  exhaust  valve  on  the  other  side. 
As  shown  in  the  figures,  all  valves  are  operated  by  vertical 


170 


GAS  POWER 


push  rods  with  the  addition  of  levers  at  the  top  in  the  cases 
of  the  admission  and  the  fuel  valves. 

These  push  rods  are  arranged  in  groups  of  three,  one 
group  for  each  cylinder,  as  shown  in  Fig.  55  (a).  Reading 
from  left  to  right  in  that  figure,  they  are  admission-valve 


FIG.  55  (a). — Side  Elevation  of  the  Busch-Sulzer  Diesel  Engine. 

push  rod,  exhaust-valve  push  rod  and  fuel- valve  push  rod. 
On  the  first  cylinder  an  extra  rod  is  installed  to  control 
the  admission  of  starting  air  as  shown  in  Fig.  55  (a).  This 
extra  rod  is  put  into  operation  and  the  fuel-valve  rod  is 
put  out  of  operation  by  means  of  the  starting-cam  shifter 
shown  beneath  the  first  cylinder  in  Fig.  55  (a). 


XIII.     MODERN  TYPES  OF  OIL  ENGINES 


171 


The  fuel  is  supplied  to  the  fuel  valves  by  means  of  fuel 
pumps,  there  being  one  pump  for  each  cylinder.  These 
are  shown  at  the  right-hand  end  of  the  engine  in  Fig.  55  (a). 
They  are  operated  by  eccentrics  on  a  shaft  geared  to  the 
cam  shaft. 


Cjl.  Head  Top  Plate 


Admission  Valw 


-Injection  Air 

'alve  Cage 

Needle 
Spring  Cap 


StaWlng"Wreuoh 
Cam  ShifUrJovsc 


FIG.  55  (6). — Section  of  the  Busch-Sulzer  Diesel  Engine. 

The  pumps  are  so  timed  that  a  charge  of  oil  is  delivered 
to  the  fuel  valve  of  each  cylinder  (through  connections 
not  shown  in  the  figure)  before  the  completion  of  the  com- 
pression stroke  in  that  cylinder.  At  the  end  of  the  com- 
pression stroke,  the  fuel  needle  is  raised  and  the  fuel  charge 
is  driven  into  the  air  in  the  cylinder  in  a  very  finely  divided 


172  GAS  POWER 

("  atomized  ")  condition.  The  compression  pressure  and 
the  temperature  in  Diesel  engines  are  so  high  that  ignition 
is  spontaneous  and  the  fuel  burns  at  about  the  rate  at  which 
it  is  injected.  No  igniting  device  is  therefore  required. 

Injection  of  fuel  continues  during  about  the  first  tenth 
of  the  stroke  at  full  load.  The  quantity  deposited  in  the 
fuel  valves,  and  hence  injected  into  the  cylinder,  is  reduced 
by  governor  action  for  fractional  loads. 

The  fuel  valve  is  water  jacketed  to  prevent  abnormal 
heating,  which  would  impair  the  mechanical  action  and 
might  cause  the  cracking  of  certain  fuels. 

In  the  type  of  Diesel  engine  here  illustrated  the  air  used 
for  blasting  the  fuel  is  compressed  by  a  separate  air  com- 
pressor. In  other  types  the  air  compressor  is  often  incor- 
porated in  the  structure  of  the  engine  and  driven  from  the 
crank  shaft.  Such  pumps  are  made  to  compress  in  two  or 
three  stages,  depending  on  the  maximum  pressure  desired. 
This  pressure  varies  with  the  character  and  quantity  of 
fuel;  with  light,  mobile  fuels  at  fractional  loads,  pressures 
of  the  order  of  600  to  700  pounds  per  square  inch  are  used, 
but  for  very  heavy,  viscous  fuels  at  full  load,  pressures 
greater  than  1000  pounds  have  sometimes  been  found 
necessary. 


CHAPTER  XIV 
GAS-ENGINE  AUXILIARIES 

76.  Starting  Devices.  The  necessity  for  some  kind 
of  a  starting  device  for  all  types  of  gas  engines  except  the 
smallest,  is  obvious.  Up  to  about  10  or  12  h.p.  they  can 
be  started  by  hand,  either  by  simply  turning  the  fly- 
wheel over  rapidly  until  the  proper  mixture  is  drawn  in 
and  ignited,  or  else  by  drawing  in  a  new  charge,  then  revers- 
ing the  direction  of  rotation  for  part  of  a  revolution  to 
compress  it,  and  finally  operating  the  sparking  mechanism 
by  hand  to  cause  combustion. 

As  the  sizes  increase,  however,  it  becomes  impossible 
to  use  these  means  of  starting  because  of  the  power  required 
to  overcome  friction  and  to  compress  the  charge,  therefore 
other  methods  have  been  developed.  The  more  common 
systems  are  considered  in  the  following  paragraphs. 

The  most  common  as  well  as  the  most  reliable  method 
of  starting  gas  engines  of  any  size  is  by  means  of  com- 
pressed air.  In  some  of  the  smaller  sizes,  as  the  engine  is 
being  shut  down,  it  pumps  air  into  a  tank,  while  in  others 
a  small  hand-operated  air  compressor  is  used  to  charge  the 
tank.  But  for  all  the  larger  sizes  it  is  customary  to  install 
a  completely  independent,  belt-driven  air-compressor  plant. 

A  starting  pressure  of  from  100  to  250  pounds  is  employed. 
In  the  case  of  single  cylinder  engines,  this  pressure  is  applied 
to  the  piston  after  turning  the  engine  over  until  the  crank 
is  past  the  head  end  centre,  and  it  is  automatically  shut 
off  and  reapplied  until  the  flywheel  has  acquired  sufficient 
momentum  to  draw  in  and  compress  a  combustible  charge. 

173 


174  GAS  POWER 

In  multicylinder  engines  one  cylinder  may  be  used  in  this 
way  until  the  others  have  "  picked  up,"  or  the  air  valves 
may  be  so  arranged  that  air  acts  on  some  or  all  of  the  pis- 
tons until  the  flywheel  has  acquired  sufficient  momentum, 
after  which  the  air  is  shut  off  and  the  flywheel  drives  the 
engine  until  it  picks  up. 

Another  method  of  starting  gas  engines  is  known  as  the 
fuel  mixture  method,  which,  however,  is  becoming  almost 
obsolete,  except  in  the  case  of  engines  using  illuminat- 
ing gas  and  in  the  case  of  certain  automobile  engines  as 
will  be  noted  below.  The  mixture  is  admitted  to  the  cyl- 
inder (after  the  piston  has  been  set  well  up  toward  the 
beginning  of  the  expansion  stroke)  and  it  is  then  ignited, 
usually  by  means  of  a  flame  or  spark.  The  pressure, 
although  small,  is  enough  to  drive  the  piston  forward, 
after  which  regular  operation  continues. 

Some  automobile  engines  are  now  started  by  forming 
a  mixture  of  acetylene  gas  and  air  within  the  cylinders 
and  igniting  this  mixture.  The  acetylene  is  supplied  under 
pressure  from  the  tank  commonly  carried  on  an  automobile 
and  may  be  distributed  to  the  cylinders  in  proper  sequence 
to  duplicate  normal  operation  by  means  of  mechanically 
operated  valves.  Or,  it  may  be  used  to  give  one  impulse 
only,  depending  on  the  fly-wheel  to  carry  the  engine  over 
the  starting  period. 

One  of  the  simplest  and  most  satisfactory  methods, 
where  current  is  available,  is  starting  by  electricity,  which 
may  be  done  in  several  ways.  An  electric  motor  may  be 
geared  to  a  rack  on  the  flywheel,  the  motor  being  auto- 
matically thrown  out  of  gear  when  the  engine  picks  up. 
Another  method,  where  the  engine  is  attached  to  a  dynamo, 
is  to  drive  the  dynamo  as  a  motor,  from  some  other  source 
of  current,  until  the  engine  has  attained  sufficient  speed 
to  take  up  its  cycle. 

In  some  plants,  where  other  engines  are  in  operation 
or  where  power  for  starting  may  be  taken  from  a  line  shaft, 


XIV.     GAS-ENGINE  AUXILIAKIES  175 

it  is  easy  to  transmit  the  motion  to  the  engine  which  is  to 
be  started.  Some  of  the  larger  installations  were  formerly 
equipped  with  small  engines,  on  the  shaft  of  which  was  a 
small  pinion  meshing  with  teeth  on  the  flywheel  of  the  large 
machine.  The  small  engine  was  automatically  disengaged 
when  the  large  machine  picked  up  its  cycle. 

77.  Mufflers.  When  an  engine  exhausts  directly  into 
the  atmosphere  it  sets  up  sound  waves  in  the  air,  because 
of  the  sudden  discharge  of  gases,  at  a  high  velocity.  The 
disagreeable  noises  resulting  are  commonly  termed  explo- 
sions. 

In  order  to  get  rid  of  these  noises  an  appliance  called 
a  muffler  is  attached  to  the  exhaust  pipe.  This  muffler 
prevents  the  sudden  impact  of  the  high-velocity  gas  directly 
upon  the  outside  atmosphere  by  causing  the  velocity  to 
be  considerably  reduced  and  by  making  the  flow  more 
nearly  continuous. 

A  very  long  plain  pipe  would  act  as  a  muffler,  since 
the  air  or  gas  contained  in  it  would  have  enough  inertia, 
and  elasticity  to  absorb  the  discharge  impacts  so  that 
the  resulting  outflow  would  be  practically  continuous.  The 
pipe  would  in  general,  however,  have  to  be  prohibitively  long, 
so  other  methods  must  be  adopted. 

The  ideal  muffler  should  convert  the  intermittent  dis- 
charges of  high  temperature  gas  into  a. perfectly  uniform 
discharge  at  a  comparatively  low  velocity  and  it  should  do 
this  without  offering  appreciable  resistance  to  the  flow, 
as  this  would  increase  the  back  pressure  on  the  engine  and 
decrease  the  power  output. 

The  gas  leaving  the  engine  has  a  high  temperature 
and  pressure  and  if  the  temperature  is  reduced  the  pressure 
will  be  reduced.  A  muffler  should,  therefore,  be  constructed 
so  as  to  reduce  the  temperature  of  the  exhaust  as  far  as 
possible.  This  is  done  by  radiation  to  the  atmosphere  in 
some  cases  and  by  water  injection  or  jacketing  in  others. 

Cooling  will  not,  in  general,  smooth  out  the  intermittent 


176 


GAS  POWER 


discharge  to  a  sufficient  extent,  and  some  sort  of  baffling 
or  expanding  devices  must  also  be  incorporated  so  as  to 
retard  high-velocity  gases  and  make  the  flow  more  nearly 


(a) 


(b) 


FIG.  56. — Types  of  Mufflers. 

continuous.  Such  baffling  devices  must  be  carefully  designed 
because  the  exhaust  gases  leaving  the  engine  may  have  a 
velocity  in  the  neighborhood  of  8000  feet  per  minute,  or, 
roughly,  90  miles  per  hour.  It  is  obvious  that  any  obstruc- 


XIV.     GAS-ENGINE  AUXILIARIES  177 

tion  in  the  exhaust  pipe  would  offer  a  large  resistance  to  the 
flow,  and  consequently  would  reduce  the  power  output 
of  the  engine  to  a  serious  extent. 

A  number  of  typical  mufflers  are  shown  in  Fig.  56.  It  will 
be  observed  that  those  shown  in  a,  b,  c,  and  d  use  baffling 
devices  to  make  the  paths  traveled  by  the  gases  long  and 
circuitous  so  that  the  gases  have  time  to  cool  and  to  lose 
part  of  their  initial  high  velocity  before  being  discharged  to 
the  atmosphere.  The  types  shown  in  6,  c  and  d  also  break 
the  gases  up  into  numerous  small  streams  which  are  so 
guided  as  to  waste  a  great  deal  of  their  velocity  energy  by 
impinging  upon  the  walls  and  upon  each  other. 

The  form  shown  in  Fig.  56  (e)  is  of  a  radically  different 
type.  The  exhaust  is  discharged  tangentially  into  a  cast- 
iron  pot  and  leaves  through  a  vertical  pipe  connected  at 
the  centre  of  that  pot.  The  high  initial  velocity  is  partly 
lost  by  cooling,  is  partly  expended  in  overcoming  its  own 
centrifugal  effect,  and  is  partly  used  to  push  away  the 
gases  already  within  the  pot.  As  a  result,  the  discharge 
from  the  central  pipe  is  fairly  steady  and  has  a  compara- 
tively low  velocity.  Perforated  baffle  plates  are  also  used 
with  this  type. 

All  mufflers  must  be  built  strong  enough  to  resist  high 
pressures  which  may  be  caused  by  the  ignition  of  a  charge 
which  was  not  burned  in  the  engine. 


CHAPTER  XV 

AMERICAN   PRACTICE   IN    THE   RATING   OF   INTERNAL- 
COMBUSTION  ENGINES 

78.  Explanatory.  The  data  contained  in  this  chapter 
are  condensed  from  the  results  of  a  very  elaborate  investiga- 
tion* of  American  practice  in  the  rating  of  stationary 
internal  combustion  engines.  As  these  results  were  de- 
duced from  a  study  of  over  six  hundred  representative 
engines,  including  the  product  of  every  well-known  American 
builder,  and  sizes  from  the  smallest  to  the  largest  made, 
it  is  thought  that  the  results  constitute  a  true  average. 

Due  to  the  large  number  of  variable  factors  entering 
into  the  design  and  rating  of  stationary  gas  engines,  it 
would  seem  at  first  impossible  to  derive  any  empirical 
formula  or  set  of  formulas  which  will  take  into  account  all 
of  these  variables  with  any  degree  of  accuracy.  However, 
it  was  found  that  such  formulas  could  be  obtained,  represent- 
ing a  grand  average  of  general  American  practice,  and 
although  not  applying  in  every  detail  to  any  one  set  of 
engines,  yet  showing  to  a  nicety  wherein  lies  the  "  safe  and 
sane  "  design. 

In  order  to  determine  average  curves  for  gas-engine 
rating,  it  is  necessary  to  consider  several  fundamental 
principles,  as:  (1)  type  of  engine,  horizontal  or  vertical;  (2) 
arrangement  and  number  of  cylinders;  (3)  kind  of  fuel 
used;  (4)  volumetric,  thermal  and  mechanical  efficiencies, 

*  Thesis,  "American  Practice  in  the  Rating  of  Internal  Combustion 
Engines,"  presented  to  Sibley  College  for  degree  of  M.M.E.  by  Messrs. 
T.  C.  Ulbricht  and  C.  E.  Torrance  in  June,  1912. 

178 


XV.    RATING  OF  INTERNAL-COMBUSTION  ENGINES     179 

etc.  These  facts  are  all  accounted  for  in  the  following 
curves  and  equations  which  are  derived  in  logical  order. 

79.  Determination  of  Rated  Brake  Horse-power.  Rated 
brake  horse-power  per  working  cylinder  end  may  be  con- 
sidered as  a  function  of  the  product  d2ln,  where  d  =  diameter 
of  cylinder  in  inches;  /  =  length  of  stroke  in  inches;  and 
n  =  r.p.m.,  so  that,  in  the  average  case,  where  the  fuel  used 
by  the  engine  is  known,  the  rated  d.h.p.  is  dependent 
upon  the  above  values. 

Fig.  57  shows  the  average  curves  obtained  for  the 
various  gases  and  fuel  oils,  by  plotting  the  values  of  the 


,_-       ^"       i-T       _T 

Values  of  d2ln 
FIG.  57. 


product  d2ln  (as  abscissa),  against  normal  rated  d.h.p. 
per  working  cylinder  end  (as  ordinates).  The  equation  of 
each  average  curve  is  given  below:* 

*  All  curves  and  equations  are  for  stationary  four-stroke  Otto 
cycle  engines  only. 


180  GAS  POWER 

For  engines  using  producer  gas: 
(1)  d.h.p.  =     -       -2.0  (average,  all  values).    .     .     .     (14) 


d.h.p.  =  LO  >  -  hor. 

17,900  and  vert,  engines) 

A  h  n  --   d*ln       4  0  (avera€e»  double-acting 
h'p-"  20,600  horizontal  engines)     '    '     * 

For  engines  using  natural  gas: 

d2ln 
d.h.p.  =  -^-^^:  —  5.0  (average  all  arrangements).    .     (17) 


For  engines  using  illuminating  gas: 

d2ln  (average,  single-acting  hori- 

"  15,700  zontal  and  vertical) 

For  engines  using  blast-furnace  gas: 


H  h  ,     -   d2ln  -  *  0  (averaSe'  double-acting 
"21,000  horizontal) 

For  engines  using  gasoline: 

,  ,  d2ln  (average,  single-acting  hori- 

"  16,400  zontal  and  vertical) 

For  engines  using  oils  and  distillates: 

d2ln      n       (average,  single-acting  hori- 
h>P'  "21,875  zontal  and  vertical) 

Where 

d.h.p.  =  rated    brake    horse-power  per    working    cylin- 
der end; 

d  =  cylinder  diameter  in  inches; 
1  =  length  of  stroke  in  inches; 
n  =  r.p.m. 


XV.     RATING  OF  INTERNAL-COMBUSTION  ENGINES     181 

Thus  it  is  evident  that  the  normal  rated  brake  horse-power 
of  an  engine  can  be  determined  when  the  cylinder  diameter, 
stroke,  r.p.m.,  and  kind  of  fuel  are  known. 

80.  To  Determine  Bore,  Stroke,  and  r.p.m.  The 
following  steps  are  convenient  in  determining  the  speed 
and  dimensions  of  an  engine  to  deliver  a  certain  power  with 
a  given  fuel: 

(a)  To  find  the  r.p.m.  The  investigation  referred  to 
showed  that  the  average  curve  for  each  type  of  engine 
takes  the  form  of  a  rectangular  hyperbola,  the  equation  of 
which  can  be  readily  determined. 

The  results  are  as  follows  : 

For    single-   and    multi-cylinder,    single-acting,    vertical 

engines: 


For  single-cylinder,  single-acting,  horizontal  engines: 

onorj 

(1)  r.p.m.  =  d  h  p  ^+128  (for  gasoline).    .     (23) 


(2)  r.p.m.  =  dhp+21  +  131  (for  gases).       .     (24) 

For  single-acting  tandem  engines: 


For  double-acting  horizontal  power  engines  (not  applicable 
to  blowing  engines): 


Having    determined    from    the    equations    the    r.p.m. 
for  the  assumed  b.h.p.  and  fuel,  substitutions  in  the  proper 


182 


GAS  POWER 


one  of  the  equations  numbered  14  through  21  will  give 
d2l  for  the  desired  engine;  so  that  it  now  remains  merely 
to  properly  proportion  the  cylinder  diameter,  d,  and  the 
stroke,  /. 

(b)  Relation  of  Stroke  to  Diameter.  The  definite  rela- 
tion between  the  cylinder  diameter  d  in  inches  (ordinate) 
and  the  length  of  stroke  I  in  inches  (abscissae),  is  shown  in 
Fig.  58,  from  which  the  following  equations  were  derived. 


0  24  6  8  10  12  14  16  18  20  22  24  26  28  30  32  34  36  38  40  42  44  46  48  50  52  54  56  58  60 

Length  of  Stroke  U)  Inches 
FIG.  58. 

For    single-    and    multi-cylinder,    single-acting,    vertical 
engines: 

d  =  0.91/-0.45 (27) 

For  single-cylinder,  single  acting,  horizontal  engines: 

d  =  0.6671+0.4 (28) 

For  single-acting  tandem  engines: 

d  =  0.772/+0.55     .     .     .     .  (29) 


XV.     KATING  OF  INTERNAL-COMBUSTION  ENGINES    183 

For  double-acting  horizontal  engines: 

(1)  d  =  0.533/+4.0  (natural  gas).      .     .     .     (30) 

(2)  d  =  0.667/4-2.0  (producer  gas)     .     .     .     (31) 

Problem.  Assume  a  100  d.h.p.  single-cylinder,  single-acting, 
horizontal  engine,  operating  on  producer  gas,  and  running  at  its 
normal  speed  for  rated  load.  Determine  the  dimensions  of  the 
above  engine  by  means  of  the  preceding  equations.  The  steps 
would  be  as  follows  : 

From  Eq.  (1), 


giving 

and  from  this 
But  from  Eq.  (24) 

giving 

and  therefore 

Now  from  Eq.  (28) 
which  gives 


d*ln  =  1,887,000.     ...         ....     (a) 


6580 


<» 


„ 


d=0.667Z+0.4, 
1=1.5^-0.6, 


184  GAS  POWER 

and  substituting  this  for  I  in  Eq.  (c)  above  gives,  after  rearrange- 
ment, 

d*-0.4d2=  6766 .715, 

from  which 

d  =  19  inches  (approx.). 

Therefore 

1  =  1.5^-0.6=28  inches. 

Hence  the  required  engine  dimensions  are: 
Cylinder  diameter  =  19"; 
Stroke  =28"; 

r.p.m.  =186"; 

d.h.p.  =100  (total). 


CHAPTER  XVI 

METHODS  OF  TESTING 

81.  Object  of  Tests.  When  the  size  of  the  engine 
permits,  tests  are  usually  made  in  the  factory  to  ascertain 
the  proper  setting  of  the  governor  for  speed  regulation; 
the  correct  timing  of  the  igniter  apparatus;  the  correct 
amount  of  compression;  the  proper  timing  of  the  valves; 
and  also  to  bring  out  any  defects  in  material  or  operation 
before  placing  the  machine  on  the  market.  The  common 
objects  of  commercial  tests  as  made  by  purchasers  are, 
however,  the  determination  of  the  power  which  the  engine 
is  capable  of  developing  and  the  fuel  consumptions  at  full 
and  fractional  loads,  i.e.,  the  fulfillment  of  contract. 

If  a  still  more  exact  knowledge  is  desired,  not  only  of 
the  engine  performance,  but  also  of  the  intricate  heat  inter- 
changes, losses,  etc.,  a  careful  laboratory  test  must  be  made 
by  a  trained  engineer. 

The  necessary  data  of  such  a  test  vary  with  the  objects 
of  the  test,  but  a  number  are  common  to  all  tests  in  which 
economy  must  be  determined.  The  data  listed  below  are 
those  which  would  be  obtained  in  a  complete  commercial 
test: 

(1)  Quantity  of  fuel  supplied. 

(2)  Calorific  value  of  fuel. 

(3)  Indicated  power. 

(4)  Developed  power. 

(5)  Quantity  of  jacket  water. 

(6)  Entering  and  exit  temperatures  of  jacket  water. 

185 


186  GAS  POWER 

(7)  Air  temperature. 

(8)  Fuel  temperature  at  engine. 

(9)  Temperature  of  exhaust  gases  at  engine. 

(10)  Barometric  pressure. 

(11)  Pressure  in  gas  and  air  pipes  at  engine. 

(12)  Speed  of  engine. 

(13)  Variation  of  speed  with  changes  of  load. 

It  is  outside  the  province  of  this  book  tck  describe  in 
detail  the  various  pieces  of  apparatus  used  for  obtaining 
the  data.  For  such  descriptions  the  reader  is  referred  to 
text-books  on  Experimental  Engineering.  It  is,  however, 
advisable  to  call  attention  to  certain  points  which  are  of 
great  importance  and  which  are  commonly  met  in  com- 
mercial testing.  These  are: 

(a)  Calorific    Value   of  Fuel.     Since   the   determination 
of  the  quantity  of  heat  consumed  by  the  engine  depends 
entirely  upon  the  measurement   of   the   quantity  of  fuel, 
and  the  determination  of  its  heating  value,  it  follows  that 
considerable   accuracy   is   necessary   at   this   point.     It   is 
never  safe  to  assume  that  the  calorific  value  of  a  fuel  during 
any  test  is  equal  to  the  average  for  that  particular  type; 
nor  is  it  safe  to  assume  it  equal  to  what  it  was  on  some 
previous  occasion.     This  is  particularly  true  in  the  case  of 
all    artificial    gases.     A    fuel    calorimeter   should    therefore 
be  used,  and  moreover  it  should  be  operated  by  one  skilled 
in  the  art  and  should  be  supplied  with  average  samples,  at 
regular  and  frequent  intervals.     It  is  not  at  all  difficult  to 
make  an  error  of  10  per  cent  by  careless   sampling   and 
improper  use  of  the  calorimeter. 

(b)  Quantity  of  Fuel.     As  just  indicated,  the  determina- 
tion of  the  quantity  of  fuel  is  just  as  important  as  that  of 
the  calorific  value.     Liquid  fuels  are  commonly  measured 
by  weighing,  but  some  sort  of  meter  or  equivalent  must  be 
used  with  gases. 

With  small  engines,  gas  meters  of  the  ordinary  type 


XVI.     METHODS  OF  TESTING  187 

may  be  made  to  give  satisfactory  results  if  proper  precau- 
tions are  taken,  but,  with  large  engines,  the  quantity  of 
fuel  used  becomes  so  great  as  to  necessitate  some  other  form 
of  measuring  device.  The  most  accurate  method  is  probably 
that  of  using  a  Venturi  meter,  though  good  results  may  be 
obtained  with  Pitot  tubes  in  skilled  hands,  and  by  the  more 
common  "  holder  drop  "  method,  when  a  gas  holder  forms 
part  of  the  installation.  In  the  "  holder  drop  "  or  displace- 
ment method,  the  gas  holder  is  calibrated  as  to  contents 
for  each  position  of  the  bell.  The  time  required  to  lower 
the  bell  from  one  position  to  another  is  then  determined, 
and  from  this  measurement  the  true  consumption  can  be 
calculated. 

It  should  *be  particularly  noted  that  all  volume  methods 
of  measuring  gases  are  materially  influenced  by  the  tem- 
perature and  pressure  of  the  gas  being  measured,  and  proper 
precautions  should  be  taken  during  measurements  and 
calculations  to  eliminate  error  from  this  source.  It  is  also 
important  to  see  that  consumption  and  calorific  value 
are  reduced  to  the  same  temperature  and  pressure  condi- 
tions before  multiplying  to  obtain  the  heat  supplied. 

(c)  Measurement  of  Developed  Horse-power.     The  direct 
measurement  of  the  developed  horse-power  of  engines  of 
moderate  size  running  at  moderate  speeds  is  easily  effected 
by  means  of  the  Prony  brake  or  other  similar  dynamometer. 
But  for  small  engines  running  at  high  speeds  and  for  large 
engines,    such    apparatus    is    not    satisfactory.     For   small 
high-speed  engines  such  as  auto  engines,  it  is  best  to  use  a 
water,  fan,  or  electric  dynamometer,  especially  constructed 
for  such  purposes.     In  the  case  of  large  engines,  it  is  generally 
impossible  to  obtain  a  direct  measurement  of  this  item,  and 
some  roundabout  means  must  then  be  employed,   as,  for 
instance,  the  measurement  of    the  output  of   a  direct-con- 
nected generator  of  known  efficiency. 

(d)  Method  of  Stating  Results.     The  economy  of  engines 
is  often  stated  in  terms  of  the  quantity  of  fuel  used  per  brake 


188  GAS  POWER 

horse-power  hour,  or  other  convenient  unit.  It  is,  however, 
more  exact  and  more  satisfactory,  particularly  in  the 
case  of  gaseous  fuels,  to  state  the  consumption  in  terms 
of  B.t.u.  consumed  per  developed  horse-power  hour  (or 
kilowatt  hour),  stating,  if  necessary,  a  minimum  calorific 
value  below  which  the  fuel  should  not  fall. 

Governor  regulation  is  generally  stated  in  terms  of  a 
percentage  variation  from  normal  speed  and  particular 
care  is  necessary  to  define  what  is  meant.  Some  engineers 
and  builders  refer  to  a  percentage  variation  each  side  of 
the  normal,  whereas  others  will  speak  of  a  percentage 
variation  in  the  same  way,  when  they  mean  total  varia- 
tion, counting  that  on  both  sides  of  the  normal.  It  is 
obvious  that  the  variation  covered  by  the  first  method  is 
approximately  twice  that  covered  by  the  second. 


CHAPTER  XVII 
PERFORMANCE  OF  AMERICAN  ENGINES 

82.  Fuel  Consumption.  During  a  recent  investiga- 
tion *  the  following  data,  showing  the  guarantees  on  the 
fuel  consumption  of  their  engines,  were  obtained  from 
American  manufacturers.  In  almost  all  cases  the  values 
are  on  the  safe  side,  as  actual  fests  show  much  better  results. 
This  underrating  the  economy  of  engines  is  the  tendency 
of  nearly  all  American  builders  to-day,  as  experience  has 
shown  it  to  be  the  safest  course. 

These  guarantees  have  the  following  ranges  for  the 
various  types  of  fuels : 

(a)  Producer  Gas. 

(1)  At  full  load: 

9370  B.t.u.  to  13,500  B.t.u.  per  d.h.p.  hour. 
75  to  100  cu.ft.  gas  per  d.h.p.  hour. 
1.12  Ibs.  to  1.25  Ibs.  coal  as  fired. 

(2)  At  f  load: 

11,000  B.t.u.  to  13,000  B.t.u.  per  d.h.p.  hour. 
(3) At  i  load: 

12,250  B.t.u.  to  16,000  B.t.u.  per  d.h.p.  hour. 
(4)  At  iload: 

17,000  B.t.u.  up,  per  d.h.p.  hour. 

(b)  Natural  Gas. 
(1)  At  full  load: 

8000  B.t.u.  to  15,300  B.t.u.  per  d.h.p.  hour. 
10  to  18  cu.ft.  gas  per  d.h.p.  hour. 

*  See  footnote  page  178. 

189 


190  GAS  POWER 

(2)  At  f  load: 

10,700  B.t.u.  to  12,000  B.t.u.  per  d.h.p.  hour. 

(3)  At  i  load: 

12,250  B.t.u.  to  16,000  B.t.u.  per  d.h.p.  hour. 

(4)  At  i  load. 

17,000  B.t.u.  up,  per  d.h.p.  hour. 

(c)  Illuminating  Gas. 

(1)  At  full  load: 

10,000  B.t.u.  to  13,000  B.t.u.  per  d.h.p.  ^hour. 
15  to  20  cu.ft.  gas  per  d.h.p.  hour. 

(2)  At  f  load: 

11,000  B.t.u.  to  12,000  B.t.u.  per  d.h.p.  hour. 

(3)  At  J  load: 

13,000  to  16,000  B.t.u.  per  d.h.p.  hour. 

(d)  Blast  Furnace  Gas. 

(1)  At  full  load: 

10,500  B.t.u.  per  d.h.p.  hour. 

(2)  At  f  load: 

11,500  B.t.u.  per  d.h.p.  hour. 

(3)  At  J  load: 

13,600  B.t.u.  per  d.h.p.  hour. 

(e)  Kerosene. 
At  full  load: 

13,240  B.t.u.  to  16,150   B.t.u.  per  d.h.p.  hour. 
yV  gal.  or  0.75  Ib.  to  0.84  Ib.  per  d.h.p.  hour  for 

small  engines. 
0.56  Ib.   to   0.65   Ib.   per   d.h.p.   hour  for  large 

engines. 
0.725  pint  to  0.901  pint  per  d.h.p.  hour. 

(f)  Gasoline. 
At  full  load: 

10,820  B.t.u.  to  15,500  B.t.u.  per  d.h.p.  hour. 
|  gal.  to  TV  gal-  Per  d.h.p.  hour. 
0.586  Ib.  to  0.968  Ib.  per  d.h.p.  hour. 
0.80  pint  to  1.10  pint  per  d.h.p.  hour. 


XVII.     PERFORMANCE  OF  AMERICAN  ENGINES     191 


(g)  Fuel  Oils  in  Otto  Cycle  Engines. 
At  full  load: 

8720  B.t.u.  to  13,320  B.t.u.  per  d.h.p.  hour. 

0.100  gal.  to  0.128  gal.,  per  d.h.p.  hour. 

0.393  Ib.  to  0.74  Ib.  per  d.h.p.  hour. 

1  pint  average  per  d.h.p.  hour. 
(h)  Fuel  Oils  in  Diesel  and  Diesel  Type  Engines. 
At  full  load: 

9029  B.t.u.  to  11,200  b.t.u.  per  d.h.p.  hour. 

0.0608  gal.  to  0.0784  gal.  per  d.h.p.  hour. 

0.447  Ib.  to  0.588  Ib.  per  d.h.p.  hour. 


inati 


ist-F- 


VT 


tusol 


I 


0   ^10    20    30    40    50    60    70    80    90  100  110  120  130  140  150  160  170  180  190  200 
D.H.P.  per  Cylinder  Per  End 

FIG.  59. — Thermal  Efficiency  Curves  (on  Brake). 

83.  Thermal  Efficiency  Curves.  From  the  data  given 
in  the  preceding  article,  thermal  efficiencies  on  the  brake 
were  calculated  (in  most  cases)  from  the  formula, 

2545 

Thermal  efficiency  =  - — — — .    .     .     (32) 

B.t.u.  per  d.h.p. 

and  the  results  plotted  as  in  Fig.  59.* 

*  A  recent  comprehensive  test  on  a  "  Pierce- Arrow "  48-h.p.  auto- 
mobile motor,  showed  a  maximum  thermal  efficiency  at  from  1100  to 
1400  r.p.m.,  of  17.8  per  cent  with  muffler  on  and  throttle  wide  open. 
With  the  throttle  one-third  open  the  thermal  efficiency  was  15.1  per  cent; 
and  6.2  per  cent  with  throttle  one-sixth  open. 


192  GAS  POWER 

84.  Consumption  of  Lubricating  Oils.     It  is  customary 
to  allow  a  consumption    of  from    0.0015  to  0.010  pint  of 
cylinder  lubricating  oil,  per  horse-power  hour  and  of  0.001 
to  0.030  pint  of  ordinary  lubricating  oil  for  bearings,  etc. 
per  horse-power  hour.     The  great  variation  in  these  figures 
is  due  to  the  difference  in  types  of  engines,  methods  of 
lubrication,  and  personal  equations  of  the  attendants.     The 
smaller   figures   are   obtained   when   the   oil   is   recovered, 
filtered  and  re-used. 

85.  Cooling  Water.     The  consumption  of  cooling  water 
has  already  been  discussed  in  Chapter  VI,  in  which  it  was 
shown   that   average   consumptions   range   from  37   to  75 
Ibs.  per  d.h.p.  hour,  in  cases  where  the  water  is  allowed  to 
run  to  waste. 


CHAPTER  XVIII 
PRACTICAL  OPERATION 

86.  Sensitiveness  of  Engine.     Internal  combustion  en- 
gines have  always  had  the  reputation  of  being  unreliable, 
but  public  opinion  in  this  respect  is  rapidly  changing  in 
view  of  the  remarkable  reliability  shown  by  the  modern 
auto  and  marine  engines,  and  by  the  better  class  of  sta- 
tionary engines.     It  must  be  admitted  that  the  internal 
combustion    engine    is    more    sensitive    to    maladjustment 
than  are  those  of  the  external  combustion  type,  but  exper- 
ience has  shown  that  intelligent  attendance  is  all  that  is 
required  to  counteract  this  weakness. 

It  has  often  been  said  in  favor  of  internal  combustion, 
that  such  engines  are  so  sensitive  to  maladjustment  that 
if  they  operate  at  all  it  must  be  at  the  highest  efficiency 
possible,  while  with  external  combustion  engines,  operation 
can  be  continued  under  almost  any  conditions  of  efficiency. 
The  first  part  of  this  statement  is  greatly  exaggerated,  as 
the  following  paragraphs  will  show. 

87.  Effect  of  Jacket  Temperature.     Most  engines  can 
be   operated   at   widely   different   jacket   temperatures   by 
simply    changing   the    amount    of   water    circulated.     For 
each    engine,    however,    there    is    some    best    temperature 
which  should  be  approximately  maintained.     Determination 
of   the   value  of   this  temperature  is  largely  a  matter  of 
experience,  but  certain  guiding  principles  can  be  set  down. 

(a)  Other  things  being  equal,  the  higher  the  jacket  tem- 
perature, the  higher  should  be  the  thermal  efficiency  of  the 
engine  because  of  the  better  combustion  phenomena  and  the 

193 


194  GAS  POWER 

decreased  loss  to  the  jacket.  The  thermal  efficiency  does 
not,  however,  increase  as  rapidly  as  might  be  expected, 
because  increased  jacket  temperature  causes  increased  loss 
in  the  exhaust,  and,  beyond  a  certain  point,  increased 
friction  losses. 

(6)  With  fuels  subject  to  preignition  and  used  in  engines 
with  high  compression,  a  high  jacket  temperature  may  cause 
trouble  because  of  insufficient  cooling  during  compression. 
Thus  engines  which  compress  a  mixture  of  air  and  liquid 
petroleum  fuels  call  for  a  low  jacket  temperature  xif  high 
compression  is  to  be  used.  The  temperature  cannot  be 
kept  too  low,  however,  as  there  would  then  be  trouble  from 
condensation  of  the  fuel  on  the  cool  cylinder  walls  just  as 
water  condenses  from  the  air  upon  a  cold  surface. 

(c)  The    power    capacity    of   an    engine   will    generally 
be  slightly  increased  as  the  jacket  temperature  is  raised 
from  very  low  to  higher  values  because  of  improved  com- 
bustion   phenomena    in    the    warmer   cylinder,    but   great 
increase  of  temperature  will  often  cause  a  reversal  of  this 
phenomenon  because  of  heating  of  the  charge  during  suc- 
tion, thus  decreasing  the  weight  per  cycle. 

(d)  Small  engines  can  generally  be  operated  with  higher 
jacket  temperatures  than  large  ones  for  the  two  following 
reasons:    first,  in  the  small  sizes  a  larger  cooling  surface 
exists  in  proportion  to  the  cylinder  content  and  therefore 
the  cooling  is  more  effective;    second,  the  castings  of  large 
engines  are  generally  more  complicated  than  those  of  small 
ones  and  they  are  more  subject  to  casting  strains  of  a  serious 
nature;   they  are  also  operated  under  much  higher  stresses. 
It  is,  therefore,  desirable  to  maintain  a  comparatively  low 
temperature  in  order  that  stresses  due  to  uneven  cooling 
and  differential  expansion  may  be  kept  as  small  as  possible. 

88.  Effect  of  Varying  Time  of  Ignition.  Experience 
has  shown  that  ignition  must  occur  before  the  end  of  the 
compression  in  all  engines  in  order  that  combustion  may  be 
nearly  completed  by  the  time  the  expansion  curve  starts. 


XVIII.     PRACTICAL  OPERATION 


195 


This  is  because  of  the  fact  that  it  takes  an  appreciable 
time  for  the  flame  to  spread  through  the  entire  charge.  The 
greater  the  quantity  of  hydrogen  or  light  hydrocarbons 
in  the  fuel,  the  more  rapid  is  the  flame  propagation  and  the 
later  may  ignition  occur.  The  more  nearly  the  combustible 
constituent  approaches  pure  carbon  monoxide  the  slower 
the  propagation  and  the  earlier  ignition  must  occur. 

The  time  element  and  the  size  of  cylinder  are  obviously 
the  controlling  features  with  any  given  mixture.  With 
high  speed,  the  time  available  is  short  and  ignition  must 
occur  very  early,  while  with  a  large  cylinder  diameter, 
the  flame  must  travel  a  great  distance  and  hence  early 


Atmos 


(a)  Normal  Ignition  (&)  Early  Iguition  (c)  Late  Ignition 

FIG.  60. — Effect  of  Varying  the  Time  of  Ignition. 

ignition  is  required.  These  effects  can  be  partly  overcome 
by  igniting  at  two  or  more  points  at  the  same  time,  so  that 
the  distance  through  which  the  flame  must  be  transmitted 
is  correspondingly  reduced.  Such  multiple  ignition  arrange- 
ments nearly  always  produce  a  gain  in  the  thermal  efficiency 
of  the  engine  because  of  the  more  rapid  combustion  and  the 
smaller  loss  to  the  jackets. 

The  diagrams  obtained  with  varying  times  of  ignition 
have  been  briefly  discussed  in  Chapter  V,  and  have  been 
illustrated  in  Fig.  11.  In  Fig.  60  are  given  three  diagrams 
obtained  in  an  actual  test.  The  first  shows  a  normal  time 
of  ignition,  the  second  extremely  early  ignition,  and  the 
third  very  late  ignition. 


196  GAS  POWER 

The  quality  of  the  mixture  also  has  an  effect  upon  the 
correct  time  of  ignition.  Extremely  lean  and  very  rich 
mixtures  are  both  slower  burning  than  the  normal  charge, 
and  both,  therefore,  require  early  ignition. 

Such  mixtures,  even  when  properly  ignited,  will  often 
continue  burning  after  the  opening  of  the  exhaust  valve, 
and  in  some  instances,  such  combustion  may  continue 
until  after  the  opening  of  the  admission  valve.  This  phenom- 
enon often  results  in  back  firing,  that  is,  in  ignition  of 
the  incoming  charge. 

89.  Effect  of  Leaky  Piston  and  Valves.     The  efficiency 
of  internal  combustion  engines  depends  on  the  compression 
pressure  if  the  pressure  at  the  beginning  of  the  compression 
stroke   remains   constant,    and,   therefore,    anything  which 
lowers  the  compression  pressure  lowers  the  thermal  efficiency. 
Leaky  pistons  and  valves  must  then  result  in  lowered  thermal 
efficiency.     There  may  be  a  further  loss  of  efficiency  due 
to  the  actual  loss  of  fuel  to  the  atmosphere  in  the  case  of  a 
leaky  piston  or  exhaust  valve. 

Leaky  parts  will  also  decrease  the  power  of  the  engine 
both  by  loss  of  charge  before  ignition  and  by  loss  of  high 
pressure  gases  after  ignition. 

Further  results  of  leaky  pistons  and  valves  are  often 
found  in  erratic  back  firing  and  explosions  in  the  exhaust 
pipe  and  muffler.  The  first  can  be  caused  by  an  inlet 
valve  overheated  by  the  leakage  of  gases,  combined  with 
the  effect  of  the  hot  gases  themselves;  the  second  by  the 
ignition  of  an  unburned  charge  which  has  leaked  by  the 
exhaust  valve. 

90.  Effect  of  Excessive  Cylinder  Lubrication.     The  in- 
terior of  the  cylinder  walls  of  internal  combustion  engines 
requires  lubrication   on  the  parts  traversed  by  the  piston 
in  order  that  friction  and  wear  may  be  reduced  to  a  min- 
imum.    The  thin  film  of  oil  which  is  spread  over  these 
walls  is  exposed  to  hot  gases  during  every  expansion  stroke, 
and  as  a  result  is  partly  burned  and  partly  "  cracked." 


XVIII.     PRACTICAL  OPERATION  197 

The  cracking  results  in  the  formation  of  carbon  and  heavy 
viscous  liquids  which  will  ultimately  impair,  or  even  pre- 
vent, the  operation  of  the  engine.  Such  material  collect- 
ing in  the  combustion  space  generally  acquires  a  high  tem- 
perature and  will  ultimately  cause  preignition;  collecting 
in  the  piston  ring  grooves  it  will  prevent  the  free  motion 
of  the  rings  and  cause  leakage. 

That  part  of  the  oil  which  burns  must  take  its  oxygen 
from  the  air  in  the  combustible  mixture  and  it  is  obvious 
that  there  is  therefore  a  limit  to  the  amount  which  can  be 
burned  in  this  way.  An  excessive  supply  of  oil  must  then 
result  in  the  retention  of  considerable  quantities  within 
the  cylinder  and  the  ultimate  cracking  thereof.  The  result 
will  be  a  smoky  exhaust,  preignitions,  carbon  deposits,  and 
inoperative  piston  rings. 

When  horizontal  engines  are  arranged  with  the  exhaust 
valve  at  the  bottom  of  the  cylinder,  most  of  the  loose  car- 
bon collecting  in  the  clearance  space  will  be  blown  out 
automatically  with  the  exhaust.  When  these  valves  are 
not  so  located,  it  is  customary  to  install  a  blowoff  cock  at 
the  lowest  point  so  that  loose  carbon  can  be  blown  out 
periodically. 

91.  Timing  of  Valves.  In  earlier  chapters  it  was  assumed 
that  admission  and  exhaust  valves  could  be  opened  suddenly 
and  to  their  full  extent,  at  the  ends  of  the  various  strokes, 
and  that  satisfactory  operation  would  result.  Such  is,  how- 
ever, far  from  true;  the  valves  of  real  engines  seldom  open 
and  close  exactly  at  the  ends  of  the  stroke  and  never 
open  or  close  suddenly  to  their  full  extent. 

The  fact  that  the  exhaust  valve  is  opened  early  (from 
85  to  90  per  cent  of  stroke)  has  already  been  mentioned. 
This  is  done  to  allow  some  of  the  gas  to  blow  out  under  the 
driving  force  of  its  own  high  pressure  and  thus  reduce  the 
pressure  and  negative  work  during  the  return  stroke.  It 
has  the  further  advantage  of  giving  a  fairly  large  valve 
opening  by  the  beginning  of  the  exhaust  stroke,  thus  de- 


198  GAS  POWER 

creasing  the  throttling  loss  during  the  early  part  of  that 
stroke. 

The  exhaust  valve,  in  practice,  is  seldom  completely 
closed  at  the  end  of  the  exhaust  stroke,  such  closure  not 
occurring  until  the  crank  has  rotated  a  number  of  degrees 
by  dead  centre.  The  burned  gases  acquire  a  high  velocity 
during  the  exhaust  period  and  by  leaving  the  valve  open 
in  this  way  the  outflow  will  continue  because  of  the  inertia 
of  the  gas  column  even  after  the  piston  has  started  on  the 
next  (suction)  stroke.  More  perfect  scavenging  is  effected 
in  this  way. 

In  the  case  of  engines  in  which  the  valves  are  widely 
separated  it  is  very  common  practice  to  open  the  inlet 
valve  before  the  exhaust  valve  has  closed,  in  many  cases 
even  before  the  exhaust  stroke  is  completed.  This  permits 
of  wider  opening  of  the  valve  in  the  early  part  of  the  suction 
stroke  and  also  takes  advantage  of  the  inertia  of  the  exhaust 
gases,  the  outrush  of  which  will  often  lower  the  pressure 
within  the  cylinder  to  a  sufficient  extent  to  assist  in  over- 
coming the  inertia  of  the  new  charge. 

Similarly,  the  inlet  valve  does  not  close  at  the  end  of 
the  suction  stroke,  but  remains  open  until  the  piston  has 
started  its  return.  In  this  way  advantage  is  taken  of  the 
inertia  of  the  incoming  column  of  gas,  thus  allowing  it  to 
pack  itself  into  the  cylinder  by  virtue  of  its  own  momentum. 

The  amount  of  overlap  in  the  valve  timing,  that  is,  the 
length  of  time  during  which  both  valves  are  open,  is  deter- 
mined by  the  valve  location  and  by  the  speed.  It  is 
greatest  with  valves  widely  separated  and  with  highest 
engine  speeds  for  obvious  reasons. 


INDEX 


A 

PAGE 

Acetylene  mixture 174 

Aero-type  engines 119 

Air  and  wrater  gas 15 

Air  cooling  (see  Cooling) 54 

Alcohol 12 

American  Car  Wheel  Co.,  engine 137-142 

American  fuel  oils,  table  of  average  values 12 

American  practice  in  the  rating  of  internal  combustion  engines .    178-184 

Anthracite  coal 9 

Artificial  gases  (see  Fuels,  gaseous) 14 

Auto  engines 118 

Auxilaries,  gas  engine 173-177 

Average  analyses  of  American  fuel  oils  (Table  I) 12 

Average  analyses  of  American  gases  (Table  II) 18 


B 

Back-firing 128 

Baume  hydrometer 11 

Beau  de  Rochas'  cycle 26 

Bench  gas 16 

Bessemer  gas  engine 134-137 

Bituminous  coal 9 

Blast-furnace  as  gas  producer 113 

Blast-furnace  gas 14 

Blower,  steam 104 

Bore,  determination  of  cylinder 181-184 

Bosch,  make  and  break  plug 79 

199 


200  INDEX 

PAGE 

Brake  horse-power,  ratings  of  American  engines 179-181 

Brayton  engine    29 

British  Thermal  Unit .* 2 

Bruce-Macbeth  engine 142-145 

Bubbling  carbureters 86 

Buckeye  engine 146-152 

Busch-Sulzer  Diesel  engine 168-172 


C 

Calorific  value  of  fuel 186 

Carbureters 85-95 

bubbling 86 

gasoline .85 

jet 86 

carbureting  valve 87 

"  float-feed  " 89 

necessity  for 85 

puddle  carbureters 86,  91 

wick  carbureters 86 

Carbureting  kerosene 91 

difficulties  of 92 

Use  of  water  in 93 

Carbureting  valve 87 

Carbureted  water  gas 16 

Charcoal 8 

Chemistry  of  producer  gas 97-102 

Classification  of  modern  engines 115-121 

On  basis  of  fuel  used 116,  117 

On  basis  of  use 117,  118 

Cleaning  apparatus  for  producers 112 

Clerk  engine 33 

Coal 8 

Classification 9 

Coke-oven  gas 16 

Cold  gas  efficiency 99 

Combustion,  external 19 

Combustion,  internal 21 

Compressed-air  starting 173 

Construction,  mechanical,  of  modern  engines 119 

Consumption  of  fuel,  by  American  engines 189-191 


INDEX  201 

PAGE 

Consumption  of  lubricating  oils  by  American  engines 192 

Conversion  of  heat  energy  into  mechanical  energy 2 

Cooling, 

Methods  of 54 

Air  cooling 54 

advantages 55 

disadvantages 56 

forced 54 

natural 54 

Forced  circulation 59 

Oil  cooling 56 

water  cooling 56 

hopper-cooling 57 

natural  circulation 56 

advantages  of 57 

disadvantages 58 

tank  cooling 58 

Cooling  of  gas  producers 99 

Cooling  water 192 

reclamation  of 61 

"  Cracking  " 93 

Crude  petroleum 10 

Cut-off  governing  (see  Governing) 71 

Cycle,  Beau  de  Rochas' 26 

Cylinder  arrangement 120 

Cylinder,  lubrication,  excessive 196-197 

D 

Diesel  cycle,  thermal  efficiency 52 

Diesel  oil  engine 33,  51,  168-172 

Distillates 11 

Double-zone  producers  (see  Producers) Ill 

Down-draft  producers  (see  Producers) 107 

Dowson  producer  gas 14 

E 

Efficiency, 

Cold  gas,  producer 99 

Thermal : 6,  21,  52 

American  engines 191 

Diesel  engines 52 

Otto  cycle 38 

Overall .  .  21 


202  INDEX 

PAGE 

Electric  ignition  (see  Ignition) 75 

Electrical  starting  device 174 

Elyria  oil  engine 163-168 

Engines,  heat 4 

Brayton 29 

Clerk 33 

Diesel 33,51 

Free-piston 28 

Gunpowder 25 

Lenoir 26 

Otto ^ 31 

Otto  and  Langen 28 

Engine  operation 193 

Effect  of  excessive  cylinder  lubrication 196-197 

effect  of  jacket  temperature 193-194 

effect  of  leaky  piston  and  valves 196 

effect  of  varying  time  of  ignition 194-195 

Timing  of  valves 197-198 

Engine,  sensitiveness  of 193 

Engine,  testing 185-188 

Engine  types, 

Areo-type 119 

Auto.' 119 

Marine 118 

Portable .118 

Stationary 117 

External  combustion , ,  19 


F 

Fairbanks-Morse  Marine  engine 126-131 

"  Float-feed  "  carbureter 89 

Fly-ball  governor 66 

Foos  gas  engine 131-134 

Foot-pound,  unit  of  work 3 

Formulae  on  rating  of  American  engines 179-181 

Four-stroke,  actual  indicator  card 38 

Four-stroke,  comparison  with  two-stroke 48 

Four-stroke,  diagram,  modifications 40 

Four-stroke,  Otto  cycle 34 

Free-piston  engine 28 


INDEX  203 

PAGE 

Fuel,  a  source  of  heat 3 

,  calorific  value 186 

consumption 189-192 

Fuels,  solid, 

Charcoal 8 

Coal 8 

Solid  wastes 10 

Wood  and  vegetable  fibres 7 

Liquid 

Petroleum  products 10 

Crude  petroleum 10 

Distillates 11 

Gasoline 11 

Kerosene 11 

Alcohol 12 

Fuels,  gaseous, 

Natural  gas 13 

Artificial  gases 14 

Blast-furnace 14 

Coke-oven 14 

Illuminating 14 

Oil  gas 14 

Producer 14 

"  Fuel-mixture  "-starting  device 174 

Fuel  oils,  table  of  average  American  values 12 


G 

Gas  and  gasoline  engines,  modern  types  (see  Modern  types). .  .  .  122-152 

Gas  engine  auxiliaries 173-177 

Gas  engine  rating 178-184 

Gas  producers 96-114 

Gaseous  fuels 13-17 

Gases  (see  Fuels,  gaseous) 13 

Gasoline  carbureters  (see  Carbureters) 85-95 

Gasolines 11 

Governing 63 

methods 64 

Hit  and  miss 65-67 

Methods  involving  cycle  variation 67 

Quality 67-70,  72 


204  INDEX 

PAGE 

Governing  methods,  quantity 67,  70 

cut-off 71,  72 

throttling 71 

mixed 72 

purpose 63 

Governors, 

fly-ball 66 

pendulum 65 

Graphite 9 

Gunpowder  engines •    25 


H 

Heat  energy  converted  into  mechanical  energy 2 

Heat  engines  and  heat  power  plants 4 

Heat  from  fuel 3 

Heat  unit,  B.t.u 2 

High-tension  system 80-84 

Higher  heating  value  of  gases 12 

Hit  and  miss  governing 65 

Hornsby-Akroyd  oil  engine 157-161 

Horse-power,  rating  on  brake 178-184 

Hot-tube  ignition , 73 


I 

Igniters,  hammer  "  make-and-break  " 77,  78 

Ignition,  effect  of  varying  time  of 194-195 

Ignition  systems 73 

electric 75 

low  tension .  76 

make-and-break 77 

hammer 77 

wipe-spark 78 

high  tension 80 

with  trembler  coil 82 

hot-tube 73 

open-flame 73 

Indicator  card,  actual,  four-stroke 38 

Internal  combustion .  .                                                           21 


INDEX  205 


Jacket  temperatures,  effect  of 193-194 

Jet  carbureters 86 

Joule's  equivalent 3 


K 

Kerosene 11 

kerosene  carbureting  of  (see  Carbureting) 91 


L 

Leaky  piston  and  valves .... 196 

Lenoir  engine . .............  26 

Lignite,  brown  and  black 9 

Liquid  fuel  problem 85 

Liquid  fuels 10-13 

alcohol 12 

distillates 11 

gasoline 11 

kerosene 11 

light  products 11 

petroleum  products 10 

Lower  heating  value  of  gases 12 

Low  tension  ignition 76 

Lubricating  oils,  consumption  of 192 

Lubrication,  excessive  cylinder «. 196-197 


M 

Make-and-break  ignition  (see  Ignition) 77 

Marine  engines 118 

Measurement  of  D.H.P 18V 

Mechanical  construction  of  modern  engines 119 

Mechanical  energy,  from  heat  energy 2 

Methods  of  governing  (see  Governing) 64 

Methods  of  stating  results  of  engine  tests 187-188 

Mixed  gas,  or  air  and  water  gas 15 

Mixed  governing 72 


206  INDEX 

PAGE 

Modern  types  of  gas  and  gasoline  engines 122-152 

American  Car  Wheel  Co 137-142 

Bessemer,  two-stroke 134-137 

Bruce-Macbeth  gas 142-145 

Buckeye 146-152 

Fairbanks-Morse  marine 126-131 

Foos  horizontal 131-134 

Fierce-Arrow  auto  engine 122-126 

Modern  types  of  oil  engines 153-172 

Diesel  oil 168-172 

Elyria  oil .*  163-168 

Hornsby-Akroyd  oil 157-161 

Muncie  oil 161-163 

Peterson  kerosene 153-157 

Modifications,  four-stroke  diagram 40 

Modifications,  two-stroke  diagram 48 

Modification  of  producer  for  different  fuels 106 

Mond  producer  gas 14 

Mufflers 175-177 

types  of 176 

Muncie  oil  engine 161-163 

N 

Natural  gas 13 

Need  of  mechanical  power 1 


O 

Oil  cooling 54 

Oil  engines,  modern  types 153-172 

Oil  gas 16 

Oils,  lubricating,  consumption  of 192 

Oil  gas  r.s.  vaporized  oil .  17 

Open-flame  ignition 73 

Operation,  practical 193-198 

Otto  cycle: 

four-stroke 34 

thermal  efficiency 38 

two-stroke 41 

Otto  engine 31 

Otto  and  Langen  engine 28 

Over-nil  thermal  efficiency 21 


INDEX  207 

P 

PAGE 

Peat 9 

Pendulum  governor 65 

Peterson  kerosene  engines 153-157 

Petroleum  products 10 

Pierce-Arrow  auto  engine 122-126 

Piston,  leaky 196 

Portable  engines 118 

Power  starting 174,  175 

Practical  operation 193-198 

Precision  governing,  advantages  and  disadvantages  (see  Govern- 
ing)       72 

Producer  cleaning  apparatus 112 

Producer  gas 14,  96 

Producer,  modified  for  different  fuels 106 

Producer,  types  of 102-114 

Ackerlund 109,  110 

double-zone Ill 

down-draft 107 

Fairbanks-Morse 103 

Loomis-Pettibone 108 

pressure 104 

R.  D.  Wood 105 

suction 102 

Westinghouse 111-112 

Puddle  carbureters 86,  91 


Quality  governing  (see  Governing) 60-70,  72 

Quantity  governing  (see  Governing) 67,  70 

Quantity  of  fuel  used  in  testing  engines  (measurement  of) ...    186,  187 


R 

R.P.M.  determination  of 181-184 

Rating  of  American  engines 178-184 

Rated  brake  horse-power 179-181 

Reactions  of  producer  gas 97-99 

Reclamation  of  cooling  water 61 


208  INDEX 

PAGE 

Refining 11 

Relation  of  stroke  to  diameter 182 

Retort  gases 14,  16 

bench  gas •. 16 

coke-oven  gas 16 

Retort  process ' 17 

Riche",  producer  gas 14 


;   ::<;;  S 

Scavenging 45 

Sensitiveness  of  engines 193 

Siemens  producer  gas 14 

Solid  fuels : 7-10 

Solid  wastes 10 

Source  of  heat,  fuel 3 

Starting  devices 173-174 

Stationary  engines 117 

Steam  blower 104 

Stroke,  determination  of 181-184 

Suction  producer,  (see  Producer) .   102 


T 

Table  1 12 

Table  II 18 

Testing  of  engines 185-188 

calorific  value  of  fuel 186 

measurement  of  D.H.P 187 

method  of  stating  results 187-188 

necessary  data 185-186 

object 185 

quantity  of  fuel 186-187 

Thermal  efficiency 6,  21,  52 

curves 191 

Otto  cycle 38 

Throttling  governing  (see  Governing) 71 

Timing,  adjustment  of 84 

Timing  of  valves 197-198 


INDEX  209 

PAGE 

Two-stroke  diagram 48 

comparison  with  four-stroke 48 

modification 48 

Two-stroke  operation,  Otto  cycle 41 


U 

Unit  of  heat,  B.t.u 2 

Unit  of  work,  foot-pound 3 


V 

Valves,  leaky 196 

Valves,  timing 197-198 

Vaporized  oil  vs.  oil  gas 17 

Vegetable  fibres 7 


W 

Wastes,  solid 10 

Water  cooling  (see  Cooling) 56 

Water  gas 15 

carbureted 16 

Water  used  for  cooling 192 

Wet-blast  gas 101 

Wick  carbureters 86 

Wipe-spark  ignition  plug 78 

Wood 9 

Wood  and  vegetables 7 

Work..  2 


THE  WILEY  TECHNICAL  SERIES 

EDITED     BY 

J.   M.  JAMESON 


A  series  of  carefully  adapted  texts  for  use  in  technical, 
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jsrvBBsm  OF  CALIFORNIA 


LAST  DATE 


29  1918 
OCT  161918 
OCT  30  19$ 


DEC19t?16 
AU$25  1919 


OCT    7  t930 


MAY   2    1948 


DE6  14  1930 


30m-6,'U 


259672 


